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 /*
  *  kernel/cpuset.c
  *
  *  Processor and Memory placement constraints for sets of tasks.
  *
  *  Copyright (C) 2003 BULL SA.
  *  Copyright (C) 2004-2007 Silicon Graphics, Inc.
  *  Copyright (C) 2006 Google, Inc
  *
  *  Portions derived from Patrick Mochel's sysfs code.
  *  sysfs is Copyright (c) 2001-3 Patrick Mochel
  *
  *  2003-10-10 Written by Simon Derr.
  *  2003-10-22 Updates by Stephen Hemminger.
  *  2004 May-July Rework by Paul Jackson.
  *  2006 Rework by Paul Menage to use generic cgroups
  *  2008 Rework of the scheduler domains and CPU hotplug handling
  *       by Max Krasnyansky
  *
  *  This file is subject to the terms and conditions of the GNU General Public
  *  License.  See the file COPYING in the main directory of the Linux
  *  distribution for more details.
  */
 
 #include <linux/cpu.h>
 #include <linux/cpumask.h>
 #include <linux/cpuset.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/kmod.h>
 #include <linux/list.h>
 #include <linux/mempolicy.h>
 #include <linux/mm.h>
 #include <linux/memory.h>
 #include <linux/export.h>
 #include <linux/mount.h>
 #include <linux/fs_context.h>
 #include <linux/namei.h>
 #include <linux/pagemap.h>
 #include <linux/proc_fs.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
 #include <linux/sched/deadline.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/task.h>
 #include <linux/seq_file.h>
 #include <linux/security.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/stat.h>
 #include <linux/string.h>
 #include <linux/time.h>
 #include <linux/time64.h>
 #include <linux/backing-dev.h>
 #include <linux/sort.h>
 #include <linux/oom.h>
 #include <linux/sched/isolation.h>
 #include <linux/uaccess.h>
 #include <linux/atomic.h>
 #include <linux/mutex.h>
 #include <linux/cgroup.h>
 #include <linux/wait.h>
 
 DEFINE_STATIC_KEY_FALSE(cpusets_pre_enable_key);
 DEFINE_STATIC_KEY_FALSE(cpusets_enabled_key);
 
 /*
  * There could be abnormal cpuset configurations for cpu or memory
  * node binding, add this key to provide a quick low-cost judgment
  * of the situation.
  */
 DEFINE_STATIC_KEY_FALSE(cpusets_insane_config_key);
 
 /* See "Frequency meter" comments, below. */
 
 struct fmeter {
     int cnt;        /* unprocessed events count */
     int val;        /* most recent output value */
     time64_t time;      /* clock (secs) when val computed */
     spinlock_t lock;    /* guards read or write of above */
 };
 
 struct cpuset {
     struct cgroup_subsys_state css;
 
     unsigned long flags;        /* "unsigned long" so bitops work */
 
     /*
      * On default hierarchy:
      *
      * The user-configured masks can only be changed by writing to
      * cpuset.cpus and cpuset.mems, and won't be limited by the
      * parent masks.
      *
      * The effective masks is the real masks that apply to the tasks
      * in the cpuset. They may be changed if the configured masks are
      * changed or hotplug happens.
      *
      * effective_mask == configured_mask & parent's effective_mask,
      * and if it ends up empty, it will inherit the parent's mask.
      *
      *
      * On legacy hierarchy:
      *
      * The user-configured masks are always the same with effective masks.
      */
 
     /* user-configured CPUs and Memory Nodes allow to tasks */
     cpumask_var_t cpus_allowed;
     nodemask_t mems_allowed;
 
     /* effective CPUs and Memory Nodes allow to tasks */
     cpumask_var_t effective_cpus;
     nodemask_t effective_mems;
 
     /*
      * CPUs allocated to child sub-partitions (default hierarchy only)
      * - CPUs granted by the parent = effective_cpus U subparts_cpus
      * - effective_cpus and subparts_cpus are mutually exclusive.
      *
      * effective_cpus contains only onlined CPUs, but subparts_cpus
      * may have offlined ones.
      */
     cpumask_var_t subparts_cpus;
 
     /*
      * This is old Memory Nodes tasks took on.
      *
      * - top_cpuset.old_mems_allowed is initialized to mems_allowed.
      * - A new cpuset's old_mems_allowed is initialized when some
      *   task is moved into it.
      * - old_mems_allowed is used in cpuset_migrate_mm() when we change
      *   cpuset.mems_allowed and have tasks' nodemask updated, and
      *   then old_mems_allowed is updated to mems_allowed.
      */
     nodemask_t old_mems_allowed;
 
     struct fmeter fmeter;       /* memory_pressure filter */
 
     /*
      * Tasks are being attached to this cpuset.  Used to prevent
      * zeroing cpus/mems_allowed between ->can_attach() and ->attach().
      */
     int attach_in_progress;
 
     /* partition number for rebuild_sched_domains() */
     int pn;
 
     /* for custom sched domain */
     int relax_domain_level;
 
     /* number of CPUs in subparts_cpus */
     int nr_subparts_cpus;
 
     /* partition root state */
     int partition_root_state;
 
     /*
      * Default hierarchy only:
      * use_parent_ecpus - set if using parent's effective_cpus
      * child_ecpus_count - # of children with use_parent_ecpus set
      */
     int use_parent_ecpus;
     int child_ecpus_count;
 
     /* Handle for cpuset.cpus.partition */
     struct cgroup_file partition_file;
 };
 
 /*
  * Partition root states:
  *
  *   0 - not a partition root
  *
  *   1 - partition root
  *
  *  -1 - invalid partition root
  *       None of the cpus in cpus_allowed can be put into the parent's
  *       subparts_cpus. In this case, the cpuset is not a real partition
  *       root anymore.  However, the CPU_EXCLUSIVE bit will still be set
  *       and the cpuset can be restored back to a partition root if the
  *       parent cpuset can give more CPUs back to this child cpuset.
  */
 #define PRS_DISABLED        0
 #define PRS_ENABLED     1
 #define PRS_ERROR       -1
 
 /*
  * Temporary cpumasks for working with partitions that are passed among
  * functions to avoid memory allocation in inner functions.
  */
 struct tmpmasks {
     cpumask_var_t addmask, delmask; /* For partition root */
     cpumask_var_t new_cpus;     /* For update_cpumasks_hier() */
 };
 
 static inline struct cpuset *css_cs(struct cgroup_subsys_state *css)
 {
     return css ? container_of(css, struct cpuset, css) : NULL;
 }
 
 /* Retrieve the cpuset for a task */
 static inline struct cpuset *task_cs(struct task_struct *task)
 {
     return css_cs(task_css(task, cpuset_cgrp_id));
 }
 
 static inline struct cpuset *parent_cs(struct cpuset *cs)
 {
     return css_cs(cs->css.parent);
 }
 
 /* bits in struct cpuset flags field */
 typedef enum {
     CS_ONLINE,
     CS_CPU_EXCLUSIVE,
     CS_MEM_EXCLUSIVE,
     CS_MEM_HARDWALL,
     CS_MEMORY_MIGRATE,
     CS_SCHED_LOAD_BALANCE,
     CS_SPREAD_PAGE,
     CS_SPREAD_SLAB,
 } cpuset_flagbits_t;
 
 /* convenient tests for these bits */
 static inline bool is_cpuset_online(struct cpuset *cs)
 {
     return test_bit(CS_ONLINE, &cs->flags) && !css_is_dying(&cs->css);
 }
 
 static inline int is_cpu_exclusive(const struct cpuset *cs)
 {
     return test_bit(CS_CPU_EXCLUSIVE, &cs->flags);
 }
 
 static inline int is_mem_exclusive(const struct cpuset *cs)
 {
     return test_bit(CS_MEM_EXCLUSIVE, &cs->flags);
 }
 
 static inline int is_mem_hardwall(const struct cpuset *cs)
 {
     return test_bit(CS_MEM_HARDWALL, &cs->flags);
 }
 
 static inline int is_sched_load_balance(const struct cpuset *cs)
 {
     return test_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
 }
 
 static inline int is_memory_migrate(const struct cpuset *cs)
 {
     return test_bit(CS_MEMORY_MIGRATE, &cs->flags);
 }
 
 static inline int is_spread_page(const struct cpuset *cs)
 {
     return test_bit(CS_SPREAD_PAGE, &cs->flags);
 }
 
 static inline int is_spread_slab(const struct cpuset *cs)
 {
     return test_bit(CS_SPREAD_SLAB, &cs->flags);
 }
 
 static inline int is_partition_root(const struct cpuset *cs)
 {
     return cs->partition_root_state > 0;
 }
 
 /*
  * Send notification event of whenever partition_root_state changes.
  */
 static inline void notify_partition_change(struct cpuset *cs,
                        int old_prs, int new_prs)
 {
     if (old_prs != new_prs)
         cgroup_file_notify(&cs->partition_file);
 }
 
 static struct cpuset top_cpuset = {
     .flags = ((1 << CS_ONLINE) | (1 << CS_CPU_EXCLUSIVE) |
           (1 << CS_MEM_EXCLUSIVE)),
     .partition_root_state = PRS_ENABLED,
 };
 
 /**
  * cpuset_for_each_child - traverse online children of a cpuset
  * @child_cs: loop cursor pointing to the current child
  * @pos_css: used for iteration
  * @parent_cs: target cpuset to walk children of
  *
  * Walk @child_cs through the online children of @parent_cs.  Must be used
  * with RCU read locked.
  */
 #define cpuset_for_each_child(child_cs, pos_css, parent_cs)     \
     css_for_each_child((pos_css), &(parent_cs)->css)        \
         if (is_cpuset_online(((child_cs) = css_cs((pos_css)))))
 
 /**
  * cpuset_for_each_descendant_pre - pre-order walk of a cpuset's descendants
  * @des_cs: loop cursor pointing to the current descendant
  * @pos_css: used for iteration
  * @root_cs: target cpuset to walk ancestor of
  *
  * Walk @des_cs through the online descendants of @root_cs.  Must be used
  * with RCU read locked.  The caller may modify @pos_css by calling
  * css_rightmost_descendant() to skip subtree.  @root_cs is included in the
  * iteration and the first node to be visited.
  */
 #define cpuset_for_each_descendant_pre(des_cs, pos_css, root_cs)    \
     css_for_each_descendant_pre((pos_css), &(root_cs)->css)     \
         if (is_cpuset_online(((des_cs) = css_cs((pos_css)))))
 
 /*
  * There are two global locks guarding cpuset structures - cpuset_rwsem and
  * callback_lock. We also require taking task_lock() when dereferencing a
  * task's cpuset pointer. See "The task_lock() exception", at the end of this
  * comment.  The cpuset code uses only cpuset_rwsem write lock.  Other
  * kernel subsystems can use cpuset_read_lock()/cpuset_read_unlock() to
  * prevent change to cpuset structures.
  *
  * A task must hold both locks to modify cpusets.  If a task holds
  * cpuset_rwsem, it blocks others wanting that rwsem, ensuring that it
  * is the only task able to also acquire callback_lock and be able to
  * modify cpusets.  It can perform various checks on the cpuset structure
  * first, knowing nothing will change.  It can also allocate memory while
  * just holding cpuset_rwsem.  While it is performing these checks, various
  * callback routines can briefly acquire callback_lock to query cpusets.
  * Once it is ready to make the changes, it takes callback_lock, blocking
  * everyone else.
  *
  * Calls to the kernel memory allocator can not be made while holding
  * callback_lock, as that would risk double tripping on callback_lock
  * from one of the callbacks into the cpuset code from within
  * __alloc_pages().
  *
  * If a task is only holding callback_lock, then it has read-only
  * access to cpusets.
  *
  * Now, the task_struct fields mems_allowed and mempolicy may be changed
  * by other task, we use alloc_lock in the task_struct fields to protect
  * them.
  *
  * The cpuset_common_file_read() handlers only hold callback_lock across
  * small pieces of code, such as when reading out possibly multi-word
  * cpumasks and nodemasks.
  *
  * Accessing a task's cpuset should be done in accordance with the
  * guidelines for accessing subsystem state in kernel/cgroup.c
  */
 
 DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
 
 void cpuset_read_lock(void)
 {
     percpu_down_read(&cpuset_rwsem);
 }
 
 void cpuset_read_unlock(void)
 {
     percpu_up_read(&cpuset_rwsem);
 }
 
 static DEFINE_SPINLOCK(callback_lock);
 
 static struct workqueue_struct *cpuset_migrate_mm_wq;
 
 /*
  * CPU / memory hotplug is handled asynchronously.
  */
 static void cpuset_hotplug_workfn(struct work_struct *work);
 static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);
 
 static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);
 
 static inline void check_insane_mems_config(nodemask_t *nodes)
 {
     if (!cpusets_insane_config() &&
         movable_only_nodes(nodes)) {
         static_branch_enable(&cpusets_insane_config_key);
         pr_info("Unsupported (movable nodes only) cpuset configuration detected (nmask=%*pbl)!\n"
             "Cpuset allocations might fail even with a lot of memory available.\n",
             nodemask_pr_args(nodes));
     }
 }
 
 /*
  * Cgroup v2 behavior is used on the "cpus" and "mems" control files when
  * on default hierarchy or when the cpuset_v2_mode flag is set by mounting
  * the v1 cpuset cgroup filesystem with the "cpuset_v2_mode" mount option.
  * With v2 behavior, "cpus" and "mems" are always what the users have
  * requested and won't be changed by hotplug events. Only the effective
  * cpus or mems will be affected.
  */
 static inline bool is_in_v2_mode(void)
 {
     return cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
           (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
 }
 
 /*
  * Return in pmask the portion of a task's cpusets's cpus_allowed that
  * are online and are capable of running the task.  If none are found,
  * walk up the cpuset hierarchy until we find one that does have some
  * appropriate cpus.
  *
  * One way or another, we guarantee to return some non-empty subset
  * of cpu_online_mask.
  *
  * Call with callback_lock or cpuset_rwsem held.
  */
 static void guarantee_online_cpus(struct task_struct *tsk,
                   struct cpumask *pmask)
 {
     const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
     struct cpuset *cs;
 
     if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask)))
         cpumask_copy(pmask, cpu_online_mask);
 
     rcu_read_lock();
     cs = task_cs(tsk);
 
     while (!cpumask_intersects(cs->effective_cpus, pmask)) {
         cs = parent_cs(cs);
         if (unlikely(!cs)) {
             /*
              * The top cpuset doesn't have any online cpu as a
              * consequence of a race between cpuset_hotplug_work
              * and cpu hotplug notifier.  But we know the top
              * cpuset's effective_cpus is on its way to be
              * identical to cpu_online_mask.
              */
             goto out_unlock;
         }
     }
     cpumask_and(pmask, pmask, cs->effective_cpus);
 
 out_unlock:
     rcu_read_unlock();
 }
 
 /*
  * Return in *pmask the portion of a cpusets's mems_allowed that
  * are online, with memory.  If none are online with memory, walk
  * up the cpuset hierarchy until we find one that does have some
  * online mems.  The top cpuset always has some mems online.
  *
  * One way or another, we guarantee to return some non-empty subset
  * of node_states[N_MEMORY].
  *
  * Call with callback_lock or cpuset_rwsem held.
  */
 static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
 {
     while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
         cs = parent_cs(cs);
     nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
 }
 
 /*
  * update task's spread flag if cpuset's page/slab spread flag is set
  *
  * Call with callback_lock or cpuset_rwsem held.
  */
 static void cpuset_update_task_spread_flag(struct cpuset *cs,
                     struct task_struct *tsk)
 {
     if (is_spread_page(cs))
         task_set_spread_page(tsk);
     else
         task_clear_spread_page(tsk);
 
     if (is_spread_slab(cs))
         task_set_spread_slab(tsk);
     else
         task_clear_spread_slab(tsk);
 }
 
 /*
  * is_cpuset_subset(p, q) - Is cpuset p a subset of cpuset q?
  *
  * One cpuset is a subset of another if all its allowed CPUs and
  * Memory Nodes are a subset of the other, and its exclusive flags
  * are only set if the other's are set.  Call holding cpuset_rwsem.
  */
 
 static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
 {
     return  cpumask_subset(p->cpus_allowed, q->cpus_allowed) &&
         nodes_subset(p->mems_allowed, q->mems_allowed) &&
         is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
         is_mem_exclusive(p) <= is_mem_exclusive(q);
 }
 
 /**
  * alloc_cpumasks - allocate three cpumasks for cpuset
  * @cs:  the cpuset that have cpumasks to be allocated.
  * @tmp: the tmpmasks structure pointer
  * Return: 0 if successful, -ENOMEM otherwise.
  *
  * Only one of the two input arguments should be non-NULL.
  */
 static inline int alloc_cpumasks(struct cpuset *cs, struct tmpmasks *tmp)
 {
     cpumask_var_t *pmask1, *pmask2, *pmask3;
 
     if (cs) {
         pmask1 = &cs->cpus_allowed;
         pmask2 = &cs->effective_cpus;
         pmask3 = &cs->subparts_cpus;
     } else {
         pmask1 = &tmp->new_cpus;
         pmask2 = &tmp->addmask;
         pmask3 = &tmp->delmask;
     }
 
     if (!zalloc_cpumask_var(pmask1, GFP_KERNEL))
         return -ENOMEM;
 
     if (!zalloc_cpumask_var(pmask2, GFP_KERNEL))
         goto free_one;
 
     if (!zalloc_cpumask_var(pmask3, GFP_KERNEL))
         goto free_two;
 
     return 0;
 
 free_two:
     free_cpumask_var(*pmask2);
 free_one:
     free_cpumask_var(*pmask1);
     return -ENOMEM;
 }
 
 /**
  * free_cpumasks - free cpumasks in a tmpmasks structure
  * @cs:  the cpuset that have cpumasks to be free.
  * @tmp: the tmpmasks structure pointer
  */
 static inline void free_cpumasks(struct cpuset *cs, struct tmpmasks *tmp)
 {
     if (cs) {
         free_cpumask_var(cs->cpus_allowed);
         free_cpumask_var(cs->effective_cpus);
         free_cpumask_var(cs->subparts_cpus);
     }
     if (tmp) {
         free_cpumask_var(tmp->new_cpus);
         free_cpumask_var(tmp->addmask);
         free_cpumask_var(tmp->delmask);
     }
 }
 
 /**
  * alloc_trial_cpuset - allocate a trial cpuset
  * @cs: the cpuset that the trial cpuset duplicates
  */
 static struct cpuset *alloc_trial_cpuset(struct cpuset *cs)
 {
     struct cpuset *trial;
 
     trial = kmemdup(cs, sizeof(*cs), GFP_KERNEL);
     if (!trial)
         return NULL;
 
     if (alloc_cpumasks(trial, NULL)) {
         kfree(trial);
         return NULL;
     }
 
     cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
     cpumask_copy(trial->effective_cpus, cs->effective_cpus);
     return trial;
 }
 
 /**
  * free_cpuset - free the cpuset
  * @cs: the cpuset to be freed
  */
 static inline void free_cpuset(struct cpuset *cs)
 {
     free_cpumasks(cs, NULL);
     kfree(cs);
 }
 
 /*
  * validate_change_legacy() - Validate conditions specific to legacy (v1)
  *                            behavior.
  */
 static int validate_change_legacy(struct cpuset *cur, struct cpuset *trial)
 {
     struct cgroup_subsys_state *css;
     struct cpuset *c, *par;
     int ret;
 
     WARN_ON_ONCE(!rcu_read_lock_held());
 
     /* Each of our child cpusets must be a subset of us */
     ret = -EBUSY;
     cpuset_for_each_child(c, css, cur)
         if (!is_cpuset_subset(c, trial))
             goto out;
 
     /* On legacy hierarchy, we must be a subset of our parent cpuset. */
     ret = -EACCES;
     par = parent_cs(cur);
     if (par && !is_cpuset_subset(trial, par))
         goto out;
 
     ret = 0;
 out:
     return ret;
 }
 
 /*
  * validate_change() - Used to validate that any proposed cpuset change
  *             follows the structural rules for cpusets.
  *
  * If we replaced the flag and mask values of the current cpuset
  * (cur) with those values in the trial cpuset (trial), would
  * our various subset and exclusive rules still be valid?  Presumes
  * cpuset_rwsem held.
  *
  * 'cur' is the address of an actual, in-use cpuset.  Operations
  * such as list traversal that depend on the actual address of the
  * cpuset in the list must use cur below, not trial.
  *
  * 'trial' is the address of bulk structure copy of cur, with
  * perhaps one or more of the fields cpus_allowed, mems_allowed,
  * or flags changed to new, trial values.
  *
  * Return 0 if valid, -errno if not.
  */
 
 static int validate_change(struct cpuset *cur, struct cpuset *trial)
 {
     struct cgroup_subsys_state *css;
     struct cpuset *c, *par;
     int ret = 0;
 
     rcu_read_lock();
 
     if (!is_in_v2_mode())
         ret = validate_change_legacy(cur, trial);
     if (ret)
         goto out;
 
     /* Remaining checks don't apply to root cpuset */
     if (cur == &top_cpuset)
         goto out;
 
     par = parent_cs(cur);
 
     /*
      * If either I or some sibling (!= me) is exclusive, we can't
      * overlap
      */
     ret = -EINVAL;
     cpuset_for_each_child(c, css, par) {
         if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
             c != cur &&
             cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
             goto out;
         if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
             c != cur &&
             nodes_intersects(trial->mems_allowed, c->mems_allowed))
             goto out;
     }
 
     /*
      * Cpusets with tasks - existing or newly being attached - can't
      * be changed to have empty cpus_allowed or mems_allowed.
      */
     ret = -ENOSPC;
     if ((cgroup_is_populated(cur->css.cgroup) || cur->attach_in_progress)) {
         if (!cpumask_empty(cur->cpus_allowed) &&
             cpumask_empty(trial->cpus_allowed))
             goto out;
         if (!nodes_empty(cur->mems_allowed) &&
             nodes_empty(trial->mems_allowed))
             goto out;
     }
 
     /*
      * We can't shrink if we won't have enough room for SCHED_DEADLINE
      * tasks.
      */
     ret = -EBUSY;
     if (is_cpu_exclusive(cur) &&
         !cpuset_cpumask_can_shrink(cur->cpus_allowed,
                        trial->cpus_allowed))
         goto out;
 
     ret = 0;
 out:
     rcu_read_unlock();
     return ret;
 }
 
 #ifdef CONFIG_SMP
 /*
  * Helper routine for generate_sched_domains().
  * Do cpusets a, b have overlapping effective cpus_allowed masks?
  */
 static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
 {
     return cpumask_intersects(a->effective_cpus, b->effective_cpus);
 }
 
 static void
 update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
 {
     if (dattr->relax_domain_level < c->relax_domain_level)
         dattr->relax_domain_level = c->relax_domain_level;
     return;
 }
 
 static void update_domain_attr_tree(struct sched_domain_attr *dattr,
                     struct cpuset *root_cs)
 {
     struct cpuset *cp;
     struct cgroup_subsys_state *pos_css;
 
     rcu_read_lock();
     cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {
         /* skip the whole subtree if @cp doesn't have any CPU */
         if (cpumask_empty(cp->cpus_allowed)) {
             pos_css = css_rightmost_descendant(pos_css);
             continue;
         }
 
         if (is_sched_load_balance(cp))
             update_domain_attr(dattr, cp);
     }
     rcu_read_unlock();
 }
 
 /* Must be called with cpuset_rwsem held.  */
 static inline int nr_cpusets(void)
 {
     /* jump label reference count + the top-level cpuset */
     return static_key_count(&cpusets_enabled_key.key) + 1;
 }
 
 /*
  * generate_sched_domains()
  *
  * This function builds a partial partition of the systems CPUs
  * A 'partial partition' is a set of non-overlapping subsets whose
  * union is a subset of that set.
  * The output of this function needs to be passed to kernel/sched/core.c
  * partition_sched_domains() routine, which will rebuild the scheduler's
  * load balancing domains (sched domains) as specified by that partial
  * partition.
  *
  * See "What is sched_load_balance" in Documentation/admin-guide/cgroup-v1/cpusets.rst
  * for a background explanation of this.
  *
  * Does not return errors, on the theory that the callers of this
  * routine would rather not worry about failures to rebuild sched
  * domains when operating in the severe memory shortage situations
  * that could cause allocation failures below.
  *
  * Must be called with cpuset_rwsem held.
  *
  * The three key local variables below are:
  *    cp - cpuset pointer, used (together with pos_css) to perform a
  *     top-down scan of all cpusets. For our purposes, rebuilding
  *     the schedulers sched domains, we can ignore !is_sched_load_
  *     balance cpusets.
  *  csa  - (for CpuSet Array) Array of pointers to all the cpusets
  *     that need to be load balanced, for convenient iterative
  *     access by the subsequent code that finds the best partition,
  *     i.e the set of domains (subsets) of CPUs such that the
  *     cpus_allowed of every cpuset marked is_sched_load_balance
  *     is a subset of one of these domains, while there are as
  *     many such domains as possible, each as small as possible.
  * doms  - Conversion of 'csa' to an array of cpumasks, for passing to
  *     the kernel/sched/core.c routine partition_sched_domains() in a
  *     convenient format, that can be easily compared to the prior
  *     value to determine what partition elements (sched domains)
  *     were changed (added or removed.)
  *
  * Finding the best partition (set of domains):
  *  The triple nested loops below over i, j, k scan over the
  *  load balanced cpusets (using the array of cpuset pointers in
  *  csa[]) looking for pairs of cpusets that have overlapping
  *  cpus_allowed, but which don't have the same 'pn' partition
  *  number and gives them in the same partition number.  It keeps
  *  looping on the 'restart' label until it can no longer find
  *  any such pairs.
  *
  *  The union of the cpus_allowed masks from the set of
  *  all cpusets having the same 'pn' value then form the one
  *  element of the partition (one sched domain) to be passed to
  *  partition_sched_domains().
  */
 static int generate_sched_domains(cpumask_var_t **domains,
             struct sched_domain_attr **attributes)
 {
     struct cpuset *cp;  /* top-down scan of cpusets */
     struct cpuset **csa;    /* array of all cpuset ptrs */
     int csn;        /* how many cpuset ptrs in csa so far */
     int i, j, k;        /* indices for partition finding loops */
     cpumask_var_t *doms;    /* resulting partition; i.e. sched domains */
     struct sched_domain_attr *dattr;  /* attributes for custom domains */
     int ndoms = 0;      /* number of sched domains in result */
     int nslot;      /* next empty doms[] struct cpumask slot */
     struct cgroup_subsys_state *pos_css;
     bool root_load_balance = is_sched_load_balance(&top_cpuset);
 
     doms = NULL;
     dattr = NULL;
     csa = NULL;
 
     /* Special case for the 99% of systems with one, full, sched domain */
     if (root_load_balance && !top_cpuset.nr_subparts_cpus) {
         ndoms = 1;
         doms = alloc_sched_domains(ndoms);
         if (!doms)
             goto done;
 
         dattr = kmalloc(sizeof(struct sched_domain_attr), GFP_KERNEL);
         if (dattr) {
             *dattr = SD_ATTR_INIT;
             update_domain_attr_tree(dattr, &top_cpuset);
         }
         cpumask_and(doms[0], top_cpuset.effective_cpus,
                 housekeeping_cpumask(HK_TYPE_DOMAIN));
 
         goto done;
     }
 
     csa = kmalloc_array(nr_cpusets(), sizeof(cp), GFP_KERNEL);
     if (!csa)
         goto done;
     csn = 0;
 
     rcu_read_lock();
     if (root_load_balance)
         csa[csn++] = &top_cpuset;
     cpuset_for_each_descendant_pre(cp, pos_css, &top_cpuset) {
         if (cp == &top_cpuset)
             continue;
         /*
          * Continue traversing beyond @cp iff @cp has some CPUs and
          * isn't load balancing.  The former is obvious.  The
          * latter: All child cpusets contain a subset of the
          * parent's cpus, so just skip them, and then we call
          * update_domain_attr_tree() to calc relax_domain_level of
          * the corresponding sched domain.
          *
          * If root is load-balancing, we can skip @cp if it
          * is a subset of the root's effective_cpus.
          */
         if (!cpumask_empty(cp->cpus_allowed) &&
             !(is_sched_load_balance(cp) &&
               cpumask_intersects(cp->cpus_allowed,
                      housekeeping_cpumask(HK_TYPE_DOMAIN))))
             continue;
 
         if (root_load_balance &&
             cpumask_subset(cp->cpus_allowed, top_cpuset.effective_cpus))
             continue;
 
         if (is_sched_load_balance(cp) &&
             !cpumask_empty(cp->effective_cpus))
             csa[csn++] = cp;
 
         /* skip @cp's subtree if not a partition root */
         if (!is_partition_root(cp))
             pos_css = css_rightmost_descendant(pos_css);
     }
     rcu_read_unlock();
 
     for (i = 0; i < csn; i++)
         csa[i]->pn = i;
     ndoms = csn;
 
 restart:
     /* Find the best partition (set of sched domains) */
     for (i = 0; i < csn; i++) {
         struct cpuset *a = csa[i];
         int apn = a->pn;
 
         for (j = 0; j < csn; j++) {
             struct cpuset *b = csa[j];
             int bpn = b->pn;
 
             if (apn != bpn && cpusets_overlap(a, b)) {
                 for (k = 0; k < csn; k++) {
                     struct cpuset *c = csa[k];
 
                     if (c->pn == bpn)
                         c->pn = apn;
                 }
                 ndoms--;    /* one less element */
                 goto restart;
             }
         }
     }
 
     /*
      * Now we know how many domains to create.
      * Convert <csn, csa> to <ndoms, doms> and populate cpu masks.
      */
     doms = alloc_sched_domains(ndoms);
     if (!doms)
         goto done;
 
     /*
      * The rest of the code, including the scheduler, can deal with
      * dattr==NULL case. No need to abort if alloc fails.
      */
     dattr = kmalloc_array(ndoms, sizeof(struct sched_domain_attr),
                   GFP_KERNEL);
 
     for (nslot = 0, i = 0; i < csn; i++) {
         struct cpuset *a = csa[i];
         struct cpumask *dp;
         int apn = a->pn;
 
         if (apn < 0) {
             /* Skip completed partitions */
             continue;
         }
 
         dp = doms[nslot];
 
         if (nslot == ndoms) {
             static int warnings = 10;
             if (warnings) {
                 pr_warn("rebuild_sched_domains confused: nslot %d, ndoms %d, csn %d, i %d, apn %d\n",
                     nslot, ndoms, csn, i, apn);
                 warnings--;
             }
             continue;
         }
 
         cpumask_clear(dp);
         if (dattr)
             *(dattr + nslot) = SD_ATTR_INIT;
         for (j = i; j < csn; j++) {
             struct cpuset *b = csa[j];
 
             if (apn == b->pn) {
                 cpumask_or(dp, dp, b->effective_cpus);
                 cpumask_and(dp, dp, housekeeping_cpumask(HK_TYPE_DOMAIN));
                 if (dattr)
                     update_domain_attr_tree(dattr + nslot, b);
 
                 /* Done with this partition */
                 b->pn = -1;
             }
         }
         nslot++;
     }
     BUG_ON(nslot != ndoms);
 
 done:
     kfree(csa);
 
     /*
      * Fallback to the default domain if kmalloc() failed.
      * See comments in partition_sched_domains().
      */
     if (doms == NULL)
         ndoms = 1;
 
     *domains    = doms;
     *attributes = dattr;
     return ndoms;
 }
 
 static void update_tasks_root_domain(struct cpuset *cs)
 {
     struct css_task_iter it;
     struct task_struct *task;
 
     css_task_iter_start(&cs->css, 0, &it);
 
     while ((task = css_task_iter_next(&it)))
         dl_add_task_root_domain(task);
 
     css_task_iter_end(&it);
 }
 
 static void rebuild_root_domains(void)
 {
     struct cpuset *cs = NULL;
     struct cgroup_subsys_state *pos_css;
 
     percpu_rwsem_assert_held(&cpuset_rwsem);
     lockdep_assert_cpus_held();
     lockdep_assert_held(&sched_domains_mutex);
 
     rcu_read_lock();
 
     /*
      * Clear default root domain DL accounting, it will be computed again
      * if a task belongs to it.
      */
     dl_clear_root_domain(&def_root_domain);
 
     cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
 
         if (cpumask_empty(cs->effective_cpus)) {
             pos_css = css_rightmost_descendant(pos_css);
             continue;
         }
 
         css_get(&cs->css);
 
         rcu_read_unlock();
 
         update_tasks_root_domain(cs);
 
         rcu_read_lock();
         css_put(&cs->css);
     }
     rcu_read_unlock();
 }
 
 static void
 partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
                     struct sched_domain_attr *dattr_new)
 {
     mutex_lock(&sched_domains_mutex);
     partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
     rebuild_root_domains();
     mutex_unlock(&sched_domains_mutex);
 }
 
 /*
  * Rebuild scheduler domains.
  *
  * If the flag 'sched_load_balance' of any cpuset with non-empty
  * 'cpus' changes, or if the 'cpus' allowed changes in any cpuset
  * which has that flag enabled, or if any cpuset with a non-empty
  * 'cpus' is removed, then call this routine to rebuild the
  * scheduler's dynamic sched domains.
  *
  * Call with cpuset_rwsem held.  Takes cpus_read_lock().
  */
 static void rebuild_sched_domains_locked(void)
 {
     struct cgroup_subsys_state *pos_css;
     struct sched_domain_attr *attr;
     cpumask_var_t *doms;
     struct cpuset *cs;
     int ndoms;
 
     lockdep_assert_cpus_held();
     percpu_rwsem_assert_held(&cpuset_rwsem);
 
     /*
      * If we have raced with CPU hotplug, return early to avoid
      * passing doms with offlined cpu to partition_sched_domains().
      * Anyways, cpuset_hotplug_workfn() will rebuild sched domains.
      *
      * With no CPUs in any subpartitions, top_cpuset's effective CPUs
      * should be the same as the active CPUs, so checking only top_cpuset
      * is enough to detect racing CPU offlines.
      */
     if (!top_cpuset.nr_subparts_cpus &&
         !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
         return;
 
     /*
      * With subpartition CPUs, however, the effective CPUs of a partition
      * root should be only a subset of the active CPUs.  Since a CPU in any
      * partition root could be offlined, all must be checked.
      */
     if (top_cpuset.nr_subparts_cpus) {
         rcu_read_lock();
         cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
             if (!is_partition_root(cs)) {
                 pos_css = css_rightmost_descendant(pos_css);
                 continue;
             }
             if (!cpumask_subset(cs->effective_cpus,
                         cpu_active_mask)) {
                 rcu_read_unlock();
                 return;
             }
         }
         rcu_read_unlock();
     }
 
     /* Generate domain masks and attrs */
     ndoms = generate_sched_domains(&doms, &attr);
 
     /* Have scheduler rebuild the domains */
     partition_and_rebuild_sched_domains(ndoms, doms, attr);
 }
 #else /* !CONFIG_SMP */
 static void rebuild_sched_domains_locked(void)
 {
 }
 #endif /* CONFIG_SMP */
 
 void rebuild_sched_domains(void)
 {
     cpus_read_lock();
     percpu_down_write(&cpuset_rwsem);
     rebuild_sched_domains_locked();
     percpu_up_write(&cpuset_rwsem);
     cpus_read_unlock();
 }
 
 /**
  * update_tasks_cpumask - Update the cpumasks of tasks in the cpuset.
  * @cs: the cpuset in which each task's cpus_allowed mask needs to be changed
  *
  * Iterate through each task of @cs updating its cpus_allowed to the
  * effective cpuset's.  As this function is called with cpuset_rwsem held,
  * cpuset membership stays stable.
  */
 static void update_tasks_cpumask(struct cpuset *cs)
 {
     struct css_task_iter it;
     struct task_struct *task;
 
     css_task_iter_start(&cs->css, 0, &it);
     while ((task = css_task_iter_next(&it)))
         set_cpus_allowed_ptr(task, cs->effective_cpus);
     css_task_iter_end(&it);
 }
 
 /**
  * compute_effective_cpumask - Compute the effective cpumask of the cpuset
  * @new_cpus: the temp variable for the new effective_cpus mask
  * @cs: the cpuset the need to recompute the new effective_cpus mask
  * @parent: the parent cpuset
  *
  * If the parent has subpartition CPUs, include them in the list of
  * allowable CPUs in computing the new effective_cpus mask. Since offlined
  * CPUs are not removed from subparts_cpus, we have to use cpu_active_mask
  * to mask those out.
  */
 static void compute_effective_cpumask(struct cpumask *new_cpus,
                       struct cpuset *cs, struct cpuset *parent)
 {
     if (parent->nr_subparts_cpus) {
         cpumask_or(new_cpus, parent->effective_cpus,
                parent->subparts_cpus);
         cpumask_and(new_cpus, new_cpus, cs->cpus_allowed);
         cpumask_and(new_cpus, new_cpus, cpu_active_mask);
     } else {
         cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus);
     }
 }
 
 /*
  * Commands for update_parent_subparts_cpumask
  */
 enum subparts_cmd {
     partcmd_enable,     /* Enable partition root     */
     partcmd_disable,    /* Disable partition root    */
     partcmd_update,     /* Update parent's subparts_cpus */
 };
 
 /**
  * update_parent_subparts_cpumask - update subparts_cpus mask of parent cpuset
  * @cpuset:  The cpuset that requests change in partition root state
  * @cmd:     Partition root state change command
  * @newmask: Optional new cpumask for partcmd_update
  * @tmp:     Temporary addmask and delmask
  * Return:   0, 1 or an error code
  *
  * For partcmd_enable, the cpuset is being transformed from a non-partition
  * root to a partition root. The cpus_allowed mask of the given cpuset will
  * be put into parent's subparts_cpus and taken away from parent's
  * effective_cpus. The function will return 0 if all the CPUs listed in
  * cpus_allowed can be granted or an error code will be returned.
  *
  * For partcmd_disable, the cpuset is being transformed from a partition
  * root back to a non-partition root. Any CPUs in cpus_allowed that are in
  * parent's subparts_cpus will be taken away from that cpumask and put back
  * into parent's effective_cpus. 0 should always be returned.
  *
  * For partcmd_update, if the optional newmask is specified, the cpu
  * list is to be changed from cpus_allowed to newmask. Otherwise,
  * cpus_allowed is assumed to remain the same. The cpuset should either
  * be a partition root or an invalid partition root. The partition root
  * state may change if newmask is NULL and none of the requested CPUs can
  * be granted by the parent. The function will return 1 if changes to
  * parent's subparts_cpus and effective_cpus happen or 0 otherwise.
  * Error code should only be returned when newmask is non-NULL.
  *
  * The partcmd_enable and partcmd_disable commands are used by
  * update_prstate(). The partcmd_update command is used by
  * update_cpumasks_hier() with newmask NULL and update_cpumask() with
  * newmask set.
  *
  * The checking is more strict when enabling partition root than the
  * other two commands.
  *
  * Because of the implicit cpu exclusive nature of a partition root,
  * cpumask changes that violates the cpu exclusivity rule will not be
  * permitted when checked by validate_change().
  */
 static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd,
                       struct cpumask *newmask,
                       struct tmpmasks *tmp)
 {
     struct cpuset *parent = parent_cs(cpuset);
     int adding; /* Moving cpus from effective_cpus to subparts_cpus */
     int deleting;   /* Moving cpus from subparts_cpus to effective_cpus */
     int old_prs, new_prs;
     bool part_error = false;    /* Partition error? */
 
     percpu_rwsem_assert_held(&cpuset_rwsem);
 
     /*
      * The parent must be a partition root.
      * The new cpumask, if present, or the current cpus_allowed must
      * not be empty.
      */
     if (!is_partition_root(parent) ||
        (newmask && cpumask_empty(newmask)) ||
        (!newmask && cpumask_empty(cpuset->cpus_allowed)))
         return -EINVAL;
 
     /*
      * Enabling/disabling partition root is not allowed if there are
      * online children.
      */
     if ((cmd != partcmd_update) && css_has_online_children(&cpuset->css))
         return -EBUSY;
 
     /*
      * Enabling partition root is not allowed if not all the CPUs
      * can be granted from parent's effective_cpus or at least one
      * CPU will be left after that.
      */
     if ((cmd == partcmd_enable) &&
        (!cpumask_subset(cpuset->cpus_allowed, parent->effective_cpus) ||
          cpumask_equal(cpuset->cpus_allowed, parent->effective_cpus)))
         return -EINVAL;
 
     /*
      * A cpumask update cannot make parent's effective_cpus become empty.
      */
     adding = deleting = false;
     old_prs = new_prs = cpuset->partition_root_state;
     if (cmd == partcmd_enable) {
         cpumask_copy(tmp->addmask, cpuset->cpus_allowed);
         adding = true;
     } else if (cmd == partcmd_disable) {
         deleting = cpumask_and(tmp->delmask, cpuset->cpus_allowed,
                        parent->subparts_cpus);
     } else if (newmask) {
         /*
          * partcmd_update with newmask:
          *
          * delmask = cpus_allowed & ~newmask & parent->subparts_cpus
          * addmask = newmask & parent->effective_cpus
          *           & ~parent->subparts_cpus
          */
         cpumask_andnot(tmp->delmask, cpuset->cpus_allowed, newmask);
         deleting = cpumask_and(tmp->delmask, tmp->delmask,
                        parent->subparts_cpus);
 
         cpumask_and(tmp->addmask, newmask, parent->effective_cpus);
         adding = cpumask_andnot(tmp->addmask, tmp->addmask,
                     parent->subparts_cpus);
         /*
          * Return error if the new effective_cpus could become empty.
          */
         if (adding &&
             cpumask_equal(parent->effective_cpus, tmp->addmask)) {
             if (!deleting)
                 return -EINVAL;
             /*
              * As some of the CPUs in subparts_cpus might have
              * been offlined, we need to compute the real delmask
              * to confirm that.
              */
             if (!cpumask_and(tmp->addmask, tmp->delmask,
                      cpu_active_mask))
                 return -EINVAL;
             cpumask_copy(tmp->addmask, parent->effective_cpus);
         }
     } else {
         /*
          * partcmd_update w/o newmask:
          *
          * addmask = cpus_allowed & parent->effective_cpus
          *
          * Note that parent's subparts_cpus may have been
          * pre-shrunk in case there is a change in the cpu list.
          * So no deletion is needed.
          */
         adding = cpumask_and(tmp->addmask, cpuset->cpus_allowed,
                      parent->effective_cpus);
         part_error = cpumask_equal(tmp->addmask,
                        parent->effective_cpus);
     }
 
     if (cmd == partcmd_update) {
         int prev_prs = cpuset->partition_root_state;
 
         /*
          * Check for possible transition between PRS_ENABLED
          * and PRS_ERROR.
          */
         switch (cpuset->partition_root_state) {
         case PRS_ENABLED:
             if (part_error)
                 new_prs = PRS_ERROR;
             break;
         case PRS_ERROR:
             if (!part_error)
                 new_prs = PRS_ENABLED;
             break;
         }
         /*
          * Set part_error if previously in invalid state.
          */
         part_error = (prev_prs == PRS_ERROR);
     }
 
     if (!part_error && (new_prs == PRS_ERROR))
         return 0;   /* Nothing need to be done */
 
     if (new_prs == PRS_ERROR) {
         /*
          * Remove all its cpus from parent's subparts_cpus.
          */
         adding = false;
         deleting = cpumask_and(tmp->delmask, cpuset->cpus_allowed,
                        parent->subparts_cpus);
     }
 
     if (!adding && !deleting && (new_prs == old_prs))
         return 0;
 
     /*
      * Change the parent's subparts_cpus.
      * Newly added CPUs will be removed from effective_cpus and
      * newly deleted ones will be added back to effective_cpus.
      */
     spin_lock_irq(&callback_lock);
     if (adding) {
         cpumask_or(parent->subparts_cpus,
                parent->subparts_cpus, tmp->addmask);
         cpumask_andnot(parent->effective_cpus,
                    parent->effective_cpus, tmp->addmask);
     }
     if (deleting) {
         cpumask_andnot(parent->subparts_cpus,
                    parent->subparts_cpus, tmp->delmask);
         /*
          * Some of the CPUs in subparts_cpus might have been offlined.
          */
         cpumask_and(tmp->delmask, tmp->delmask, cpu_active_mask);
         cpumask_or(parent->effective_cpus,
                parent->effective_cpus, tmp->delmask);
     }
 
     parent->nr_subparts_cpus = cpumask_weight(parent->subparts_cpus);
 
     if (old_prs != new_prs)
         cpuset->partition_root_state = new_prs;
 
     spin_unlock_irq(&callback_lock);
     notify_partition_change(cpuset, old_prs, new_prs);
 
     return cmd == partcmd_update;
 }
 
 /*
  * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
  * @cs:  the cpuset to consider
  * @tmp: temp variables for calculating effective_cpus & partition setup
  *
  * When configured cpumask is changed, the effective cpumasks of this cpuset
  * and all its descendants need to be updated.
  *
  * On legacy hierarchy, effective_cpus will be the same with cpu_allowed.
  *
  * Called with cpuset_rwsem held
  */
 static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp)
 {
     struct cpuset *cp;
     struct cgroup_subsys_state *pos_css;
     bool need_rebuild_sched_domains = false;
     int old_prs, new_prs;
 
     rcu_read_lock();
     cpuset_for_each_descendant_pre(cp, pos_css, cs) {
         struct cpuset *parent = parent_cs(cp);
 
         compute_effective_cpumask(tmp->new_cpus, cp, parent);
 
         /*
          * If it becomes empty, inherit the effective mask of the
          * parent, which is guaranteed to have some CPUs.
          */
         if (is_in_v2_mode() && cpumask_empty(tmp->new_cpus)) {
             cpumask_copy(tmp->new_cpus, parent->effective_cpus);
             if (!cp->use_parent_ecpus) {
                 cp->use_parent_ecpus = true;
                 parent->child_ecpus_count++;
             }
         } else if (cp->use_parent_ecpus) {
             cp->use_parent_ecpus = false;
             WARN_ON_ONCE(!parent->child_ecpus_count);
             parent->child_ecpus_count--;
         }
 
         /*
          * Skip the whole subtree if the cpumask remains the same
          * and has no partition root state.
          */
         if (!cp->partition_root_state &&
             cpumask_equal(tmp->new_cpus, cp->effective_cpus)) {
             pos_css = css_rightmost_descendant(pos_css);
             continue;
         }
 
         /*
          * update_parent_subparts_cpumask() should have been called
          * for cs already in update_cpumask(). We should also call
          * update_tasks_cpumask() again for tasks in the parent
          * cpuset if the parent's subparts_cpus changes.
          */
         old_prs = new_prs = cp->partition_root_state;
         if ((cp != cs) && old_prs) {
             switch (parent->partition_root_state) {
             case PRS_DISABLED:
                 /*
                  * If parent is not a partition root or an
                  * invalid partition root, clear its state
                  * and its CS_CPU_EXCLUSIVE flag.
                  */
                 WARN_ON_ONCE(cp->partition_root_state
                          != PRS_ERROR);
                 new_prs = PRS_DISABLED;
 
                 /*
                  * clear_bit() is an atomic operation and
                  * readers aren't interested in the state
                  * of CS_CPU_EXCLUSIVE anyway. So we can
                  * just update the flag without holding
                  * the callback_lock.
                  */
                 clear_bit(CS_CPU_EXCLUSIVE, &cp->flags);
                 break;
 
             case PRS_ENABLED:
                 if (update_parent_subparts_cpumask(cp, partcmd_update, NULL, tmp))
                     update_tasks_cpumask(parent);
                 break;
 
             case PRS_ERROR:
                 /*
                  * When parent is invalid, it has to be too.
                  */
                 new_prs = PRS_ERROR;
                 break;
             }
         }
 
         if (!css_tryget_online(&cp->css))
             continue;
         rcu_read_unlock();
 
         spin_lock_irq(&callback_lock);
 
         cpumask_copy(cp->effective_cpus, tmp->new_cpus);
         if (cp->nr_subparts_cpus && (new_prs != PRS_ENABLED)) {
             cp->nr_subparts_cpus = 0;
             cpumask_clear(cp->subparts_cpus);
         } else if (cp->nr_subparts_cpus) {
             /*
              * Make sure that effective_cpus & subparts_cpus
              * are mutually exclusive.
              *
              * In the unlikely event that effective_cpus
              * becomes empty. we clear cp->nr_subparts_cpus and
              * let its child partition roots to compete for
              * CPUs again.
              */
             cpumask_andnot(cp->effective_cpus, cp->effective_cpus,
                        cp->subparts_cpus);
             if (cpumask_empty(cp->effective_cpus)) {
                 cpumask_copy(cp->effective_cpus, tmp->new_cpus);
                 cpumask_clear(cp->subparts_cpus);
                 cp->nr_subparts_cpus = 0;
             } else if (!cpumask_subset(cp->subparts_cpus,
                            tmp->new_cpus)) {
                 cpumask_andnot(cp->subparts_cpus,
                     cp->subparts_cpus, tmp->new_cpus);
                 cp->nr_subparts_cpus
                     = cpumask_weight(cp->subparts_cpus);
             }
         }
 
         if (new_prs != old_prs)
             cp->partition_root_state = new_prs;
 
         spin_unlock_irq(&callback_lock);
         notify_partition_change(cp, old_prs, new_prs);
 
         WARN_ON(!is_in_v2_mode() &&
             !cpumask_equal(cp->cpus_allowed, cp->effective_cpus));
 
         update_tasks_cpumask(cp);
 
         /*
          * On legacy hierarchy, if the effective cpumask of any non-
          * empty cpuset is changed, we need to rebuild sched domains.
          * On default hierarchy, the cpuset needs to be a partition
          * root as well.
          */
         if (!cpumask_empty(cp->cpus_allowed) &&
             is_sched_load_balance(cp) &&
            (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
             is_partition_root(cp)))
             need_rebuild_sched_domains = true;
 
         rcu_read_lock();
         css_put(&cp->css);
     }
     rcu_read_unlock();
 
     if (need_rebuild_sched_domains)
         rebuild_sched_domains_locked();
 }
 
 /**
  * update_sibling_cpumasks - Update siblings cpumasks
  * @parent:  Parent cpuset
  * @cs:      Current cpuset
  * @tmp:     Temp variables
  */
 static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
                     struct tmpmasks *tmp)
 {
     struct cpuset *sibling;
     struct cgroup_subsys_state *pos_css;
 
     percpu_rwsem_assert_held(&cpuset_rwsem);
 
     /*
      * Check all its siblings and call update_cpumasks_hier()
      * if their use_parent_ecpus flag is set in order for them
      * to use the right effective_cpus value.
      *
      * The update_cpumasks_hier() function may sleep. So we have to
      * release the RCU read lock before calling it.
      */
     rcu_read_lock();
     cpuset_for_each_child(sibling, pos_css, parent) {
         if (sibling == cs)
             continue;
         if (!sibling->use_parent_ecpus)
             continue;
         if (!css_tryget_online(&sibling->css))
             continue;
 
         rcu_read_unlock();
         update_cpumasks_hier(sibling, tmp);
         rcu_read_lock();
         css_put(&sibling->css);
     }
     rcu_read_unlock();
 }
 
 /**
  * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
  * @cs: the cpuset to consider
  * @trialcs: trial cpuset
  * @buf: buffer of cpu numbers written to this cpuset
  */
 static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
               const char *buf)
 {
     int retval;
     struct tmpmasks tmp;
 
     /* top_cpuset.cpus_allowed tracks cpu_online_mask; it's read-only */
     if (cs == &top_cpuset)
         return -EACCES;
 
     /*
      * An empty cpus_allowed is ok only if the cpuset has no tasks.
      * Since cpulist_parse() fails on an empty mask, we special case
      * that parsing.  The validate_change() call ensures that cpusets
      * with tasks have cpus.
      */
     if (!*buf) {
         cpumask_clear(trialcs->cpus_allowed);
     } else {
         retval = cpulist_parse(buf, trialcs->cpus_allowed);
         if (retval < 0)
             return retval;
 
         if (!cpumask_subset(trialcs->cpus_allowed,
                     top_cpuset.cpus_allowed))
             return -EINVAL;
     }
 
     /* Nothing to do if the cpus didn't change */
     if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
         return 0;
 
     retval = validate_change(cs, trialcs);
     if (retval < 0)
         return retval;
 
 #ifdef CONFIG_CPUMASK_OFFSTACK
     /*
      * Use the cpumasks in trialcs for tmpmasks when they are pointers
      * to allocated cpumasks.
      */
     tmp.addmask  = trialcs->subparts_cpus;
     tmp.delmask  = trialcs->effective_cpus;
     tmp.new_cpus = trialcs->cpus_allowed;
 #endif
 
     if (cs->partition_root_state) {
         /* Cpumask of a partition root cannot be empty */
         if (cpumask_empty(trialcs->cpus_allowed))
             return -EINVAL;
         if (update_parent_subparts_cpumask(cs, partcmd_update,
                     trialcs->cpus_allowed, &tmp) < 0)
             return -EINVAL;
     }
 
     spin_lock_irq(&callback_lock);
     cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
 
     /*
      * Make sure that subparts_cpus is a subset of cpus_allowed.
      */
     if (cs->nr_subparts_cpus) {
         cpumask_and(cs->subparts_cpus, cs->subparts_cpus, cs->cpus_allowed);
         cs->nr_subparts_cpus = cpumask_weight(cs->subparts_cpus);
     }
     spin_unlock_irq(&callback_lock);
 
     update_cpumasks_hier(cs, &tmp);
 
     if (cs->partition_root_state) {
         struct cpuset *parent = parent_cs(cs);
 
         /*
          * For partition root, update the cpumasks of sibling
          * cpusets if they use parent's effective_cpus.
          */
         if (parent->child_ecpus_count)
             update_sibling_cpumasks(parent, cs, &tmp);
     }
     return 0;
 }
 
 /*
  * Migrate memory region from one set of nodes to another.  This is
  * performed asynchronously as it can be called from process migration path
  * holding locks involved in process management.  All mm migrations are
  * performed in the queued order and can be waited for by flushing
  * cpuset_migrate_mm_wq.
  */
 
 struct cpuset_migrate_mm_work {
     struct work_struct  work;
     struct mm_struct    *mm;
     nodemask_t      from;
     nodemask_t      to;
 };
 
 static void cpuset_migrate_mm_workfn(struct work_struct *work)
 {
     struct cpuset_migrate_mm_work *mwork =
         container_of(work, struct cpuset_migrate_mm_work, work);
 
     /* on a wq worker, no need to worry about %current's mems_allowed */
     do_migrate_pages(mwork->mm, &mwork->from, &mwork->to, MPOL_MF_MOVE_ALL);
     mmput(mwork->mm);
     kfree(mwork);
 }
 
 static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
                             const nodemask_t *to)
 {
     struct cpuset_migrate_mm_work *mwork;
 
     if (nodes_equal(*from, *to)) {
         mmput(mm);
         return;
     }
 
     mwork = kzalloc(sizeof(*mwork), GFP_KERNEL);
     if (mwork) {
         mwork->mm = mm;
         mwork->from = *from;
         mwork->to = *to;
         INIT_WORK(&mwork->work, cpuset_migrate_mm_workfn);
         queue_work(cpuset_migrate_mm_wq, &mwork->work);
     } else {
         mmput(mm);
     }
 }
 
 static void cpuset_post_attach(void)
 {
     flush_workqueue(cpuset_migrate_mm_wq);
 }
 
 /*
  * cpuset_change_task_nodemask - change task's mems_allowed and mempolicy
  * @tsk: the task to change
  * @newmems: new nodes that the task will be set
  *
  * We use the mems_allowed_seq seqlock to safely update both tsk->mems_allowed
  * and rebind an eventual tasks' mempolicy. If the task is allocating in
  * parallel, it might temporarily see an empty intersection, which results in
  * a seqlock check and retry before OOM or allocation failure.
  */
 static void cpuset_change_task_nodemask(struct task_struct *tsk,
                     nodemask_t *newmems)
 {
     task_lock(tsk);
 
     local_irq_disable();
     write_seqcount_begin(&tsk->mems_allowed_seq);
 
     nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
     mpol_rebind_task(tsk, newmems);
     tsk->mems_allowed = *newmems;
 
     write_seqcount_end(&tsk->mems_allowed_seq);
     local_irq_enable();
 
     task_unlock(tsk);
 }
 
 static void *cpuset_being_rebound;
 
 /**
  * update_tasks_nodemask - Update the nodemasks of tasks in the cpuset.
  * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
  *
  * Iterate through each task of @cs updating its mems_allowed to the
  * effective cpuset's.  As this function is called with cpuset_rwsem held,
  * cpuset membership stays stable.
  */
 static void update_tasks_nodemask(struct cpuset *cs)
 {
     static nodemask_t newmems;  /* protected by cpuset_rwsem */
     struct css_task_iter it;
     struct task_struct *task;
 
     cpuset_being_rebound = cs;      /* causes mpol_dup() rebind */
 
     guarantee_online_mems(cs, &newmems);
 
     /*
      * The mpol_rebind_mm() call takes mmap_lock, which we couldn't
      * take while holding tasklist_lock.  Forks can happen - the
      * mpol_dup() cpuset_being_rebound check will catch such forks,
      * and rebind their vma mempolicies too.  Because we still hold
      * the global cpuset_rwsem, we know that no other rebind effort
      * will be contending for the global variable cpuset_being_rebound.
      * It's ok if we rebind the same mm twice; mpol_rebind_mm()
      * is idempotent.  Also migrate pages in each mm to new nodes.
      */
     css_task_iter_start(&cs->css, 0, &it);
     while ((task = css_task_iter_next(&it))) {
         struct mm_struct *mm;
         bool migrate;
 
         cpuset_change_task_nodemask(task, &newmems);
 
         mm = get_task_mm(task);
         if (!mm)
             continue;
 
         migrate = is_memory_migrate(cs);
 
         mpol_rebind_mm(mm, &cs->mems_allowed);
         if (migrate)
             cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems);
         else
             mmput(mm);
     }
     css_task_iter_end(&it);
 
     /*
      * All the tasks' nodemasks have been updated, update
      * cs->old_mems_allowed.
      */
     cs->old_mems_allowed = newmems;
 
     /* We're done rebinding vmas to this cpuset's new mems_allowed. */
     cpuset_being_rebound = NULL;
 }
 
 /*
  * update_nodemasks_hier - Update effective nodemasks and tasks in the subtree
  * @cs: the cpuset to consider
  * @new_mems: a temp variable for calculating new effective_mems
  *
  * When configured nodemask is changed, the effective nodemasks of this cpuset
  * and all its descendants need to be updated.
  *
  * On legacy hierarchy, effective_mems will be the same with mems_allowed.
  *
  * Called with cpuset_rwsem held
  */
 static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
 {
     struct cpuset *cp;
     struct cgroup_subsys_state *pos_css;
 
     rcu_read_lock();
     cpuset_for_each_descendant_pre(cp, pos_css, cs) {
         struct cpuset *parent = parent_cs(cp);
 
         nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
 
         /*
          * If it becomes empty, inherit the effective mask of the
          * parent, which is guaranteed to have some MEMs.
          */
         if (is_in_v2_mode() && nodes_empty(*new_mems))
             *new_mems = parent->effective_mems;
 
         /* Skip the whole subtree if the nodemask remains the same. */
         if (nodes_equal(*new_mems, cp->effective_mems)) {
             pos_css = css_rightmost_descendant(pos_css);
             continue;
         }
 
         if (!css_tryget_online(&cp->css))
             continue;
         rcu_read_unlock();
 
         spin_lock_irq(&callback_lock);
         cp->effective_mems = *new_mems;
         spin_unlock_irq(&callback_lock);
 
         WARN_ON(!is_in_v2_mode() &&
             !nodes_equal(cp->mems_allowed, cp->effective_mems));
 
         update_tasks_nodemask(cp);
 
         rcu_read_lock();
         css_put(&cp->css);
     }
     rcu_read_unlock();
 }
 
 /*
  * Handle user request to change the 'mems' memory placement
  * of a cpuset.  Needs to validate the request, update the
  * cpusets mems_allowed, and for each task in the cpuset,
  * update mems_allowed and rebind task's mempolicy and any vma
  * mempolicies and if the cpuset is marked 'memory_migrate',
  * migrate the tasks pages to the new memory.
  *
  * Call with cpuset_rwsem held. May take callback_lock during call.
  * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
  * lock each such tasks mm->mmap_lock, scan its vma's and rebind
  * their mempolicies to the cpusets new mems_allowed.
  */
 static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
                const char *buf)
 {
     int retval;
 
     /*
      * top_cpuset.mems_allowed tracks node_stats[N_MEMORY];
      * it's read-only
      */
     if (cs == &top_cpuset) {
         retval = -EACCES;
         goto done;
     }
 
     /*
      * An empty mems_allowed is ok iff there are no tasks in the cpuset.
      * Since nodelist_parse() fails on an empty mask, we special case
      * that parsing.  The validate_change() call ensures that cpusets
      * with tasks have memory.
      */
     if (!*buf) {
         nodes_clear(trialcs->mems_allowed);
     } else {
         retval = nodelist_parse(buf, trialcs->mems_allowed);
         if (retval < 0)
             goto done;
 
         if (!nodes_subset(trialcs->mems_allowed,
                   top_cpuset.mems_allowed)) {
             retval = -EINVAL;
             goto done;
         }
     }
 
     if (nodes_equal(cs->mems_allowed, trialcs->mems_allowed)) {
         retval = 0;     /* Too easy - nothing to do */
         goto done;
     }
     retval = validate_change(cs, trialcs);
     if (retval < 0)
         goto done;
 
     check_insane_mems_config(&trialcs->mems_allowed);
 
     spin_lock_irq(&callback_lock);
     cs->mems_allowed = trialcs->mems_allowed;
     spin_unlock_irq(&callback_lock);
 
     /* use trialcs->mems_allowed as a temp variable */
     update_nodemasks_hier(cs, &trialcs->mems_allowed);
 done:
     return retval;
 }
 
 bool current_cpuset_is_being_rebound(void)
 {
     bool ret;
 
     rcu_read_lock();
     ret = task_cs(current) == cpuset_being_rebound;
     rcu_read_unlock();
 
     return ret;
 }
 
 static int update_relax_domain_level(struct cpuset *cs, s64 val)
 {
 #ifdef CONFIG_SMP
     if (val < -1 || val >= sched_domain_level_max)
         return -EINVAL;
 #endif
 
     if (val != cs->relax_domain_level) {
         cs->relax_domain_level = val;
         if (!cpumask_empty(cs->cpus_allowed) &&
             is_sched_load_balance(cs))
             rebuild_sched_domains_locked();
     }
 
     return 0;
 }
 
 /**
  * update_tasks_flags - update the spread flags of tasks in the cpuset.
  * @cs: the cpuset in which each task's spread flags needs to be changed
  *
  * Iterate through each task of @cs updating its spread flags.  As this
  * function is called with cpuset_rwsem held, cpuset membership stays
  * stable.
  */
 static void update_tasks_flags(struct cpuset *cs)
 {
     struct css_task_iter it;
     struct task_struct *task;
 
     css_task_iter_start(&cs->css, 0, &it);
     while ((task = css_task_iter_next(&it)))
         cpuset_update_task_spread_flag(cs, task);
     css_task_iter_end(&it);
 }
 
 /*
  * update_flag - read a 0 or a 1 in a file and update associated flag
  * bit:     the bit to update (see cpuset_flagbits_t)
  * cs:      the cpuset to update
  * turning_on:  whether the flag is being set or cleared
  *
  * Call with cpuset_rwsem held.
  */
 
 static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
                int turning_on)
 {
     struct cpuset *trialcs;
     int balance_flag_changed;
     int spread_flag_changed;
     int err;
 
     trialcs = alloc_trial_cpuset(cs);
     if (!trialcs)
         return -ENOMEM;
 
     if (turning_on)
         set_bit(bit, &trialcs->flags);
     else
         clear_bit(bit, &trialcs->flags);
 
     err = validate_change(cs, trialcs);
     if (err < 0)
         goto out;
 
     balance_flag_changed = (is_sched_load_balance(cs) !=
                 is_sched_load_balance(trialcs));
 
     spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
             || (is_spread_page(cs) != is_spread_page(trialcs)));
 
     spin_lock_irq(&callback_lock);
     cs->flags = trialcs->flags;
     spin_unlock_irq(&callback_lock);
 
     if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
         rebuild_sched_domains_locked();
 
     if (spread_flag_changed)
         update_tasks_flags(cs);
 out:
     free_cpuset(trialcs);
     return err;
 }
 
 /*
  * update_prstate - update partition_root_state
  * cs: the cpuset to update
  * new_prs: new partition root state
  *
  * Call with cpuset_rwsem held.
  */
 static int update_prstate(struct cpuset *cs, int new_prs)
 {
     int err, old_prs = cs->partition_root_state;
     struct cpuset *parent = parent_cs(cs);
     struct tmpmasks tmpmask;
 
     if (old_prs == new_prs)
         return 0;
 
     /*
      * Cannot force a partial or invalid partition root to a full
      * partition root.
      */
     if (new_prs && (old_prs == PRS_ERROR))
         return -EINVAL;
 
     if (alloc_cpumasks(NULL, &tmpmask))
         return -ENOMEM;
 
     err = -EINVAL;
     if (!old_prs) {
         /*
          * Turning on partition root requires setting the
          * CS_CPU_EXCLUSIVE bit implicitly as well and cpus_allowed
          * cannot be NULL.
          */
         if (cpumask_empty(cs->cpus_allowed))
             goto out;
 
         err = update_flag(CS_CPU_EXCLUSIVE, cs, 1);
         if (err)
             goto out;
 
         err = update_parent_subparts_cpumask(cs, partcmd_enable,
                              NULL, &tmpmask);
         if (err) {
             update_flag(CS_CPU_EXCLUSIVE, cs, 0);
             goto out;
         }
     } else {
         /*
          * Turning off partition root will clear the
          * CS_CPU_EXCLUSIVE bit.
          */
         if (old_prs == PRS_ERROR) {
             update_flag(CS_CPU_EXCLUSIVE, cs, 0);
             err = 0;
             goto out;
         }
 
         err = update_parent_subparts_cpumask(cs, partcmd_disable,
                              NULL, &tmpmask);
         if (err)
             goto out;
 
         /* Turning off CS_CPU_EXCLUSIVE will not return error */
         update_flag(CS_CPU_EXCLUSIVE, cs, 0);
     }
 
     /*
      * Update cpumask of parent's tasks except when it is the top
      * cpuset as some system daemons cannot be mapped to other CPUs.
      */
     if (parent != &top_cpuset)
         update_tasks_cpumask(parent);
 
     if (parent->child_ecpus_count)
         update_sibling_cpumasks(parent, cs, &tmpmask);
 
     rebuild_sched_domains_locked();
 out:
     if (!err) {
         spin_lock_irq(&callback_lock);
         cs->partition_root_state = new_prs;
         spin_unlock_irq(&callback_lock);
         notify_partition_change(cs, old_prs, new_prs);
     }
 
     free_cpumasks(NULL, &tmpmask);
     return err;
 }
 
 /*
  * Frequency meter - How fast is some event occurring?
  *
  * These routines manage a digitally filtered, constant time based,
  * event frequency meter.  There are four routines:
  *   fmeter_init() - initialize a frequency meter.
  *   fmeter_markevent() - called each time the event happens.
  *   fmeter_getrate() - returns the recent rate of such events.
  *   fmeter_update() - internal routine used to update fmeter.
  *
  * A common data structure is passed to each of these routines,
  * which is used to keep track of the state required to manage the
  * frequency meter and its digital filter.
  *
  * The filter works on the number of events marked per unit time.
  * The filter is single-pole low-pass recursive (IIR).  The time unit
  * is 1 second.  Arithmetic is done using 32-bit integers scaled to
  * simulate 3 decimal digits of precision (multiplied by 1000).
  *
  * With an FM_COEF of 933, and a time base of 1 second, the filter
  * has a half-life of 10 seconds, meaning that if the events quit
  * happening, then the rate returned from the fmeter_getrate()
  * will be cut in half each 10 seconds, until it converges to zero.
  *
  * It is not worth doing a real infinitely recursive filter.  If more
  * than FM_MAXTICKS ticks have elapsed since the last filter event,
  * just compute FM_MAXTICKS ticks worth, by which point the level
  * will be stable.
  *
  * Limit the count of unprocessed events to FM_MAXCNT, so as to avoid
  * arithmetic overflow in the fmeter_update() routine.
  *
  * Given the simple 32 bit integer arithmetic used, this meter works
  * best for reporting rates between one per millisecond (msec) and
  * one per 32 (approx) seconds.  At constant rates faster than one
  * per msec it maxes out at values just under 1,000,000.  At constant
  * rates between one per msec, and one per second it will stabilize
  * to a value N*1000, where N is the rate of events per second.
  * At constant rates between one per second and one per 32 seconds,
  * it will be choppy, moving up on the seconds that have an event,
  * and then decaying until the next event.  At rates slower than
  * about one in 32 seconds, it decays all the way back to zero between
  * each event.
  */
 
 #define FM_COEF 933     /* coefficient for half-life of 10 secs */
 #define FM_MAXTICKS ((u32)99)   /* useless computing more ticks than this */
 #define FM_MAXCNT 1000000   /* limit cnt to avoid overflow */
 #define FM_SCALE 1000       /* faux fixed point scale */
 
 /* Initialize a frequency meter */
 static void fmeter_init(struct fmeter *fmp)
 {
     fmp->cnt = 0;
     fmp->val = 0;
     fmp->time = 0;
     spin_lock_init(&fmp->lock);
 }
 
 /* Internal meter update - process cnt events and update value */
 static void fmeter_update(struct fmeter *fmp)
 {
     time64_t now;
     u32 ticks;
 
     now = ktime_get_seconds();
     ticks = now - fmp->time;
 
     if (ticks == 0)
         return;
 
     ticks = min(FM_MAXTICKS, ticks);
     while (ticks-- > 0)
         fmp->val = (FM_COEF * fmp->val) / FM_SCALE;
     fmp->time = now;
 
     fmp->val += ((FM_SCALE - FM_COEF) * fmp->cnt) / FM_SCALE;
     fmp->cnt = 0;
 }
 
 /* Process any previous ticks, then bump cnt by one (times scale). */
 static void fmeter_markevent(struct fmeter *fmp)
 {
     spin_lock(&fmp->lock);
     fmeter_update(fmp);
     fmp->cnt = min(FM_MAXCNT, fmp->cnt + FM_SCALE);
     spin_unlock(&fmp->lock);
 }
 
 /* Process any previous ticks, then return current value. */
 static int fmeter_getrate(struct fmeter *fmp)
 {
     int val;
 
     spin_lock(&fmp->lock);
     fmeter_update(fmp);
     val = fmp->val;
     spin_unlock(&fmp->lock);
     return val;
 }
 
 static struct cpuset *cpuset_attach_old_cs;
 
 /* Called by cgroups to determine if a cpuset is usable; cpuset_rwsem held */
 static int cpuset_can_attach(struct cgroup_taskset *tset)
 {
     struct cgroup_subsys_state *css;
     struct cpuset *cs;
     struct task_struct *task;
     int ret;
 
     /* used later by cpuset_attach() */
     cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
     cs = css_cs(css);
 
     percpu_down_write(&cpuset_rwsem);
 
     /* allow moving tasks into an empty cpuset if on default hierarchy */
     ret = -ENOSPC;
     if (!is_in_v2_mode() &&
         (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
         goto out_unlock;
 
     cgroup_taskset_for_each(task, css, tset) {
         ret = task_can_attach(task, cs->effective_cpus);
         if (ret)
             goto out_unlock;
         ret = security_task_setscheduler(task);
         if (ret)
             goto out_unlock;
     }
 
     /*
      * Mark attach is in progress.  This makes validate_change() fail
      * changes which zero cpus/mems_allowed.
      */
     cs->attach_in_progress++;
     ret = 0;
 out_unlock:
     percpu_up_write(&cpuset_rwsem);
     return ret;
 }
 
 static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 {
     struct cgroup_subsys_state *css;
 
     cgroup_taskset_first(tset, &css);
 
     percpu_down_write(&cpuset_rwsem);
     css_cs(css)->attach_in_progress--;
     percpu_up_write(&cpuset_rwsem);
 }
 
 /*
  * Protected by cpuset_rwsem.  cpus_attach is used only by cpuset_attach()
  * but we can't allocate it dynamically there.  Define it global and
  * allocate from cpuset_init().
  */
 static cpumask_var_t cpus_attach;
 
 static void cpuset_attach(struct cgroup_taskset *tset)
 {
     /* static buf protected by cpuset_rwsem */
     static nodemask_t cpuset_attach_nodemask_to;
     struct task_struct *task;
     struct task_struct *leader;
     struct cgroup_subsys_state *css;
     struct cpuset *cs;
     struct cpuset *oldcs = cpuset_attach_old_cs;
 
     cgroup_taskset_first(tset, &css);
     cs = css_cs(css);
 
     lockdep_assert_cpus_held(); /* see cgroup_attach_lock() */
     percpu_down_write(&cpuset_rwsem);
 
     guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
 
     cgroup_taskset_for_each(task, css, tset) {
         if (cs != &top_cpuset)
             guarantee_online_cpus(task, cpus_attach);
         else
             cpumask_copy(cpus_attach, task_cpu_possible_mask(task));
         /*
          * can_attach beforehand should guarantee that this doesn't
          * fail.  TODO: have a better way to handle failure here
          */
         WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
 
         cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
         cpuset_update_task_spread_flag(cs, task);
     }
 
     /*
      * Change mm for all threadgroup leaders. This is expensive and may
      * sleep and should be moved outside migration path proper.
      */
     cpuset_attach_nodemask_to = cs->effective_mems;
     cgroup_taskset_for_each_leader(leader, css, tset) {
         struct mm_struct *mm = get_task_mm(leader);
 
         if (mm) {
             mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
 
             /*
              * old_mems_allowed is the same with mems_allowed
              * here, except if this task is being moved
              * automatically due to hotplug.  In that case
              * @mems_allowed has been updated and is empty, so
              * @old_mems_allowed is the right nodesets that we
              * migrate mm from.
              */
             if (is_memory_migrate(cs))
                 cpuset_migrate_mm(mm, &oldcs->old_mems_allowed,
                           &cpuset_attach_nodemask_to);
             else
                 mmput(mm);
         }
     }
 
     cs->old_mems_allowed = cpuset_attach_nodemask_to;
 
     cs->attach_in_progress--;
     if (!cs->attach_in_progress)
         wake_up(&cpuset_attach_wq);
 
     percpu_up_write(&cpuset_rwsem);
 }
 
 /* The various types of files and directories in a cpuset file system */
 
 typedef enum {
     FILE_MEMORY_MIGRATE,
     FILE_CPULIST,
     FILE_MEMLIST,
     FILE_EFFECTIVE_CPULIST,
     FILE_EFFECTIVE_MEMLIST,
     FILE_SUBPARTS_CPULIST,
     FILE_CPU_EXCLUSIVE,
     FILE_MEM_EXCLUSIVE,
     FILE_MEM_HARDWALL,
     FILE_SCHED_LOAD_BALANCE,
     FILE_PARTITION_ROOT,
     FILE_SCHED_RELAX_DOMAIN_LEVEL,
     FILE_MEMORY_PRESSURE_ENABLED,
     FILE_MEMORY_PRESSURE,
     FILE_SPREAD_PAGE,
     FILE_SPREAD_SLAB,
 } cpuset_filetype_t;
 
 static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
                 u64 val)
 {
     struct cpuset *cs = css_cs(css);
     cpuset_filetype_t type = cft->private;
     int retval = 0;
 
     cpus_read_lock();
     percpu_down_write(&cpuset_rwsem);
     if (!is_cpuset_online(cs)) {
         retval = -ENODEV;
         goto out_unlock;
     }
 
     switch (type) {
     case FILE_CPU_EXCLUSIVE:
         retval = update_flag(CS_CPU_EXCLUSIVE, cs, val);
         break;
     case FILE_MEM_EXCLUSIVE:
         retval = update_flag(CS_MEM_EXCLUSIVE, cs, val);
         break;
     case FILE_MEM_HARDWALL:
         retval = update_flag(CS_MEM_HARDWALL, cs, val);
         break;
     case FILE_SCHED_LOAD_BALANCE:
         retval = update_flag(CS_SCHED_LOAD_BALANCE, cs, val);
         break;
     case FILE_MEMORY_MIGRATE:
         retval = update_flag(CS_MEMORY_MIGRATE, cs, val);
         break;
     case FILE_MEMORY_PRESSURE_ENABLED:
         cpuset_memory_pressure_enabled = !!val;
         break;
     case FILE_SPREAD_PAGE:
         retval = update_flag(CS_SPREAD_PAGE, cs, val);
         break;
     case FILE_SPREAD_SLAB:
         retval = update_flag(CS_SPREAD_SLAB, cs, val);
         break;
     default:
         retval = -EINVAL;
         break;
     }
 out_unlock:
     percpu_up_write(&cpuset_rwsem);
     cpus_read_unlock();
     return retval;
 }
 
 static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
                 s64 val)
 {
     struct cpuset *cs = css_cs(css);
     cpuset_filetype_t type = cft->private;
     int retval = -ENODEV;
 
     cpus_read_lock();
     percpu_down_write(&cpuset_rwsem);
     if (!is_cpuset_online(cs))
         goto out_unlock;
 
     switch (type) {
     case FILE_SCHED_RELAX_DOMAIN_LEVEL:
         retval = update_relax_domain_level(cs, val);
         break;
     default:
         retval = -EINVAL;
         break;
     }
 out_unlock:
     percpu_up_write(&cpuset_rwsem);
     cpus_read_unlock();
     return retval;
 }
 
 /*
  * Common handling for a write to a "cpus" or "mems" file.
  */
 static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
                     char *buf, size_t nbytes, loff_t off)
 {
     struct cpuset *cs = css_cs(of_css(of));
     struct cpuset *trialcs;
     int retval = -ENODEV;
 
     buf = strstrip(buf);
 
     /*
      * CPU or memory hotunplug may leave @cs w/o any execution
      * resources, in which case the hotplug code asynchronously updates
      * configuration and transfers all tasks to the nearest ancestor
      * which can execute.
      *
      * As writes to "cpus" or "mems" may restore @cs's execution
      * resources, wait for the previously scheduled operations before
      * proceeding, so that we don't end up keep removing tasks added
      * after execution capability is restored.
      *
      * cpuset_hotplug_work calls back into cgroup core via
      * cgroup_transfer_tasks() and waiting for it from a cgroupfs
      * operation like this one can lead to a deadlock through kernfs
      * active_ref protection.  Let's break the protection.  Losing the
      * protection is okay as we check whether @cs is online after
      * grabbing cpuset_rwsem anyway.  This only happens on the legacy
      * hierarchies.
      */
     css_get(&cs->css);
     kernfs_break_active_protection(of->kn);
     flush_work(&cpuset_hotplug_work);
 
     cpus_read_lock();
     percpu_down_write(&cpuset_rwsem);
     if (!is_cpuset_online(cs))
         goto out_unlock;
 
     trialcs = alloc_trial_cpuset(cs);
     if (!trialcs) {
         retval = -ENOMEM;
         goto out_unlock;
     }
 
     switch (of_cft(of)->private) {
     case FILE_CPULIST:
         retval = update_cpumask(cs, trialcs, buf);
         break;
     case FILE_MEMLIST:
         retval = update_nodemask(cs, trialcs, buf);
         break;
     default:
         retval = -EINVAL;
         break;
     }
 
     free_cpuset(trialcs);
 out_unlock:
     percpu_up_write(&cpuset_rwsem);
     cpus_read_unlock();
     kernfs_unbreak_active_protection(of->kn);
     css_put(&cs->css);
     flush_workqueue(cpuset_migrate_mm_wq);
     return retval ?: nbytes;
 }
 
 /*
  * These ascii lists should be read in a single call, by using a user
  * buffer large enough to hold the entire map.  If read in smaller
  * chunks, there is no guarantee of atomicity.  Since the display format
  * used, list of ranges of sequential numbers, is variable length,
  * and since these maps can change value dynamically, one could read
  * gibberish by doing partial reads while a list was changing.
  */
 static int cpuset_common_seq_show(struct seq_file *sf, void *v)
 {
     struct cpuset *cs = css_cs(seq_css(sf));
     cpuset_filetype_t type = seq_cft(sf)->private;
     int ret = 0;
 
     spin_lock_irq(&callback_lock);
 
     switch (type) {
     case FILE_CPULIST:
         seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->cpus_allowed));
         break;
     case FILE_MEMLIST:
         seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->mems_allowed));
         break;
     case FILE_EFFECTIVE_CPULIST:
         seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->effective_cpus));
         break;
     case FILE_EFFECTIVE_MEMLIST:
         seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->effective_mems));
         break;
     case FILE_SUBPARTS_CPULIST:
         seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->subparts_cpus));
         break;
     default:
         ret = -EINVAL;
     }
 
     spin_unlock_irq(&callback_lock);
     return ret;
 }
 
 static u64 cpuset_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
 {
     struct cpuset *cs = css_cs(css);
     cpuset_filetype_t type = cft->private;
     switch (type) {
     case FILE_CPU_EXCLUSIVE:
         return is_cpu_exclusive(cs);
     case FILE_MEM_EXCLUSIVE:
         return is_mem_exclusive(cs);
     case FILE_MEM_HARDWALL:
         return is_mem_hardwall(cs);
     case FILE_SCHED_LOAD_BALANCE:
         return is_sched_load_balance(cs);
     case FILE_MEMORY_MIGRATE:
         return is_memory_migrate(cs);
     case FILE_MEMORY_PRESSURE_ENABLED:
         return cpuset_memory_pressure_enabled;
     case FILE_MEMORY_PRESSURE:
         return fmeter_getrate(&cs->fmeter);
     case FILE_SPREAD_PAGE:
         return is_spread_page(cs);
     case FILE_SPREAD_SLAB:
         return is_spread_slab(cs);
     default:
         BUG();
     }
 
     /* Unreachable but makes gcc happy */
     return 0;
 }
 
 static s64 cpuset_read_s64(struct cgroup_subsys_state *css, struct cftype *cft)
 {
     struct cpuset *cs = css_cs(css);
     cpuset_filetype_t type = cft->private;
     switch (type) {
     case FILE_SCHED_RELAX_DOMAIN_LEVEL:
         return cs->relax_domain_level;
     default:
         BUG();
     }
 
     /* Unreachable but makes gcc happy */
     return 0;
 }
 
 static int sched_partition_show(struct seq_file *seq, void *v)
 {
     struct cpuset *cs = css_cs(seq_css(seq));
 
     switch (cs->partition_root_state) {
     case PRS_ENABLED:
         seq_puts(seq, "root\n");
         break;
     case PRS_DISABLED:
         seq_puts(seq, "member\n");
         break;
     case PRS_ERROR:
         seq_puts(seq, "root invalid\n");
         break;
     }
     return 0;
 }
 
 static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf,
                      size_t nbytes, loff_t off)
 {
     struct cpuset *cs = css_cs(of_css(of));
     int val;
     int retval = -ENODEV;
 
     buf = strstrip(buf);
 
     /*
      * Convert "root" to ENABLED, and convert "member" to DISABLED.
      */
     if (!strcmp(buf, "root"))
         val = PRS_ENABLED;
     else if (!strcmp(buf, "member"))
         val = PRS_DISABLED;
     else
         return -EINVAL;
 
     css_get(&cs->css);
     cpus_read_lock();
     percpu_down_write(&cpuset_rwsem);
     if (!is_cpuset_online(cs))
         goto out_unlock;
 
     retval = update_prstate(cs, val);
 out_unlock:
     percpu_up_write(&cpuset_rwsem);
     cpus_read_unlock();
     css_put(&cs->css);
     return retval ?: nbytes;
 }
 
 /*
  * for the common functions, 'private' gives the type of file
  */
 
 static struct cftype legacy_files[] = {
     {
         .name = "cpus",
         .seq_show = cpuset_common_seq_show,
         .write = cpuset_write_resmask,
         .max_write_len = (100U + 6 * NR_CPUS),
         .private = FILE_CPULIST,
     },
 
     {
         .name = "mems",
         .seq_show = cpuset_common_seq_show,
         .write = cpuset_write_resmask,
         .max_write_len = (100U + 6 * MAX_NUMNODES),
         .private = FILE_MEMLIST,
     },
 
     {
         .name = "effective_cpus",
         .seq_show = cpuset_common_seq_show,
         .private = FILE_EFFECTIVE_CPULIST,
     },
 
     {
         .name = "effective_mems",
         .seq_show = cpuset_common_seq_show,
         .private = FILE_EFFECTIVE_MEMLIST,
     },
 
     {
         .name = "cpu_exclusive",
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_CPU_EXCLUSIVE,
     },
 
     {
         .name = "mem_exclusive",
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_MEM_EXCLUSIVE,
     },
 
     {
         .name = "mem_hardwall",
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_MEM_HARDWALL,
     },
 
     {
         .name = "sched_load_balance",
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_SCHED_LOAD_BALANCE,
     },
 
     {
         .name = "sched_relax_domain_level",
         .read_s64 = cpuset_read_s64,
         .write_s64 = cpuset_write_s64,
         .private = FILE_SCHED_RELAX_DOMAIN_LEVEL,
     },
 
     {
         .name = "memory_migrate",
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_MEMORY_MIGRATE,
     },
 
     {
         .name = "memory_pressure",
         .read_u64 = cpuset_read_u64,
         .private = FILE_MEMORY_PRESSURE,
     },
 
     {
         .name = "memory_spread_page",
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_SPREAD_PAGE,
     },
 
     {
         .name = "memory_spread_slab",
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_SPREAD_SLAB,
     },
 
     {
         .name = "memory_pressure_enabled",
         .flags = CFTYPE_ONLY_ON_ROOT,
         .read_u64 = cpuset_read_u64,
         .write_u64 = cpuset_write_u64,
         .private = FILE_MEMORY_PRESSURE_ENABLED,
     },
 
     { } /* terminate */
 };
 
 /*
  * This is currently a minimal set for the default hierarchy. It can be
  * expanded later on by migrating more features and control files from v1.
  */
 static struct cftype dfl_files[] = {
     {
         .name = "cpus",
         .seq_show = cpuset_common_seq_show,
         .write = cpuset_write_resmask,
         .max_write_len = (100U + 6 * NR_CPUS),
         .private = FILE_CPULIST,
         .flags = CFTYPE_NOT_ON_ROOT,
     },
 
     {
         .name = "mems",
         .seq_show = cpuset_common_seq_show,
         .write = cpuset_write_resmask,
         .max_write_len = (100U + 6 * MAX_NUMNODES),
         .private = FILE_MEMLIST,
         .flags = CFTYPE_NOT_ON_ROOT,
     },
 
     {
         .name = "cpus.effective",
         .seq_show = cpuset_common_seq_show,
         .private = FILE_EFFECTIVE_CPULIST,
     },
 
     {
         .name = "mems.effective",
         .seq_show = cpuset_common_seq_show,
         .private = FILE_EFFECTIVE_MEMLIST,
     },
 
     {
         .name = "cpus.partition",
         .seq_show = sched_partition_show,
         .write = sched_partition_write,
         .private = FILE_PARTITION_ROOT,
         .flags = CFTYPE_NOT_ON_ROOT,
         .file_offset = offsetof(struct cpuset, partition_file),
     },
 
     {
         .name = "cpus.subpartitions",
         .seq_show = cpuset_common_seq_show,
         .private = FILE_SUBPARTS_CPULIST,
         .flags = CFTYPE_DEBUG,
     },
 
     { } /* terminate */
 };
 
 
 /*
  *  cpuset_css_alloc - allocate a cpuset css
  *  cgrp:   control group that the new cpuset will be part of
  */
 
 static struct cgroup_subsys_state *
 cpuset_css_alloc(struct cgroup_subsys_state *parent_css)
 {
     struct cpuset *cs;
 
     if (!parent_css)
         return &top_cpuset.css;
 
     cs = kzalloc(sizeof(*cs), GFP_KERNEL);
     if (!cs)
         return ERR_PTR(-ENOMEM);
 
     if (alloc_cpumasks(cs, NULL)) {
         kfree(cs);
         return ERR_PTR(-ENOMEM);
     }
 
     __set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
     nodes_clear(cs->mems_allowed);
     nodes_clear(cs->effective_mems);
     fmeter_init(&cs->fmeter);
     cs->relax_domain_level = -1;
 
     /* Set CS_MEMORY_MIGRATE for default hierarchy */
     if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
         __set_bit(CS_MEMORY_MIGRATE, &cs->flags);
 
     return &cs->css;
 }
 
 static int cpuset_css_online(struct cgroup_subsys_state *css)
 {
     struct cpuset *cs = css_cs(css);
     struct cpuset *parent = parent_cs(cs);
     struct cpuset *tmp_cs;
     struct cgroup_subsys_state *pos_css;
 
     if (!parent)
         return 0;
 
     cpus_read_lock();
     percpu_down_write(&cpuset_rwsem);
 
     set_bit(CS_ONLINE, &cs->flags);
     if (is_spread_page(parent))
         set_bit(CS_SPREAD_PAGE, &cs->flags);
     if (is_spread_slab(parent))
         set_bit(CS_SPREAD_SLAB, &cs->flags);
 
     cpuset_inc();
 
     spin_lock_irq(&callback_lock);
     if (is_in_v2_mode()) {
         cpumask_copy(cs->effective_cpus, parent->effective_cpus);
         cs->effective_mems = parent->effective_mems;
         cs->use_parent_ecpus = true;
         parent->child_ecpus_count++;
     }
     spin_unlock_irq(&callback_lock);
 
     if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags))
         goto out_unlock;
 
     /*
      * Clone @parent's configuration if CGRP_CPUSET_CLONE_CHILDREN is
      * set.  This flag handling is implemented in cgroup core for
      * historical reasons - the flag may be specified during mount.
      *
      * Currently, if any sibling cpusets have exclusive cpus or mem, we
      * refuse to clone the configuration - thereby refusing the task to
      * be entered, and as a result refusing the sys_unshare() or
      * clone() which initiated it.  If this becomes a problem for some
      * users who wish to allow that scenario, then this could be
      * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
      * (and likewise for mems) to the new cgroup.
      */
     rcu_read_lock();
     cpuset_for_each_child(tmp_cs, pos_css, parent) {
         if (is_mem_exclusive(tmp_cs) || is_cpu_exclusive(tmp_cs)) {
             rcu_read_unlock();
             goto out_unlock;
         }
     }
     rcu_read_unlock();
 
     spin_lock_irq(&callback_lock);
     cs->mems_allowed = parent->mems_allowed;
     cs->effective_mems = parent->mems_allowed;
     cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
     cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
     spin_unlock_irq(&callback_lock);
 out_unlock:
     percpu_up_write(&cpuset_rwsem);
     cpus_read_unlock();
     return 0;
 }
 
 /*
  * If the cpuset being removed has its flag 'sched_load_balance'
  * enabled, then simulate turning sched_load_balance off, which
  * will call rebuild_sched_domains_locked(). That is not needed
  * in the default hierarchy where only changes in partition
  * will cause repartitioning.
  *
  * If the cpuset has the 'sched.partition' flag enabled, simulate
  * turning 'sched.partition" off.
  */
 
 static void cpuset_css_offline(struct cgroup_subsys_state *css)
 {
     struct cpuset *cs = css_cs(css);
 
     cpus_read_lock();
     percpu_down_write(&cpuset_rwsem);
 
     if (is_partition_root(cs))
         update_prstate(cs, 0);
 
     if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
         is_sched_load_balance(cs))
         update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
 
     if (cs->use_parent_ecpus) {
         struct cpuset *parent = parent_cs(cs);
 
         cs->use_parent_ecpus = false;
         parent->child_ecpus_count--;
     }
 
     cpuset_dec();
     clear_bit(CS_ONLINE, &cs->flags);
 
     percpu_up_write(&cpuset_rwsem);
     cpus_read_unlock();
 }
 
 static void cpuset_css_free(struct cgroup_subsys_state *css)
 {
     struct cpuset *cs = css_cs(css);
 
     free_cpuset(cs);
 }
 
 static void cpuset_bind(struct cgroup_subsys_state *root_css)
 {
     percpu_down_write(&cpuset_rwsem);
     spin_lock_irq(&callback_lock);
 
     if (is_in_v2_mode()) {
         cpumask_copy(top_cpuset.cpus_allowed, cpu_possible_mask);
         top_cpuset.mems_allowed = node_possible_map;
     } else {
         cpumask_copy(top_cpuset.cpus_allowed,
                  top_cpuset.effective_cpus);
         top_cpuset.mems_allowed = top_cpuset.effective_mems;
     }
 
     spin_unlock_irq(&callback_lock);
     percpu_up_write(&cpuset_rwsem);
 }
 
 /*
  * Make sure the new task conform to the current state of its parent,
  * which could have been changed by cpuset just after it inherits the
  * state from the parent and before it sits on the cgroup's task list.
  */
 static void cpuset_fork(struct task_struct *task)
 {
     if (task_css_is_root(task, cpuset_cgrp_id))
         return;
 
     set_cpus_allowed_ptr(task, current->cpus_ptr);
     task->mems_allowed = current->mems_allowed;
 }
 
 struct cgroup_subsys cpuset_cgrp_subsys = {
     .css_alloc  = cpuset_css_alloc,
     .css_online = cpuset_css_online,
     .css_offline    = cpuset_css_offline,
     .css_free   = cpuset_css_free,
     .can_attach = cpuset_can_attach,
     .cancel_attach  = cpuset_cancel_attach,
     .attach     = cpuset_attach,
     .post_attach    = cpuset_post_attach,
     .bind       = cpuset_bind,
     .fork       = cpuset_fork,
     .legacy_cftypes = legacy_files,
     .dfl_cftypes    = dfl_files,
     .early_init = true,
     .threaded   = true,
 };
 
 /**
  * cpuset_init - initialize cpusets at system boot
  *
  * Description: Initialize top_cpuset
  **/
 
 int __init cpuset_init(void)
 {
     BUG_ON(percpu_init_rwsem(&cpuset_rwsem));
 
     BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL));
     BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL));
     BUG_ON(!zalloc_cpumask_var(&top_cpuset.subparts_cpus, GFP_KERNEL));
 
     cpumask_setall(top_cpuset.cpus_allowed);
     nodes_setall(top_cpuset.mems_allowed);
     cpumask_setall(top_cpuset.effective_cpus);
     nodes_setall(top_cpuset.effective_mems);
 
     fmeter_init(&top_cpuset.fmeter);
     set_bit(CS_SCHED_LOAD_BALANCE, &top_cpuset.flags);
     top_cpuset.relax_domain_level = -1;
 
     BUG_ON(!alloc_cpumask_var(&cpus_attach, GFP_KERNEL));
 
     return 0;
 }
 
 /*
  * If CPU and/or memory hotplug handlers, below, unplug any CPUs
  * or memory nodes, we need to walk over the cpuset hierarchy,
  * removing that CPU or node from all cpusets.  If this removes the
  * last CPU or node from a cpuset, then move the tasks in the empty
  * cpuset to its next-highest non-empty parent.
  */
 static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
 {
     struct cpuset *parent;
 
     /*
      * Find its next-highest non-empty parent, (top cpuset
      * has online cpus, so can't be empty).
      */
     parent = parent_cs(cs);
     while (cpumask_empty(parent->cpus_allowed) ||
             nodes_empty(parent->mems_allowed))
         parent = parent_cs(parent);
 
     if (cgroup_transfer_tasks(parent->css.cgroup, cs->css.cgroup)) {
         pr_err("cpuset: failed to transfer tasks out of empty cpuset ");
         pr_cont_cgroup_name(cs->css.cgroup);
         pr_cont("\n");
     }
 }
 
 static void
 hotplug_update_tasks_legacy(struct cpuset *cs,
                 struct cpumask *new_cpus, nodemask_t *new_mems,
                 bool cpus_updated, bool mems_updated)
 {
     bool is_empty;
 
     spin_lock_irq(&callback_lock);
     cpumask_copy(cs->cpus_allowed, new_cpus);
     cpumask_copy(cs->effective_cpus, new_cpus);
     cs->mems_allowed = *new_mems;
     cs->effective_mems = *new_mems;
     spin_unlock_irq(&callback_lock);
 
     /*
      * Don't call update_tasks_cpumask() if the cpuset becomes empty,
      * as the tasks will be migrated to an ancestor.
      */
     if (cpus_updated && !cpumask_empty(cs->cpus_allowed))
         update_tasks_cpumask(cs);
     if (mems_updated && !nodes_empty(cs->mems_allowed))
         update_tasks_nodemask(cs);
 
     is_empty = cpumask_empty(cs->cpus_allowed) ||
            nodes_empty(cs->mems_allowed);
 
     percpu_up_write(&cpuset_rwsem);
 
     /*
      * Move tasks to the nearest ancestor with execution resources,
      * This is full cgroup operation which will also call back into
      * cpuset. Should be done outside any lock.
      */
     if (is_empty)
         remove_tasks_in_empty_cpuset(cs);
 
     percpu_down_write(&cpuset_rwsem);
 }
 
 static void
 hotplug_update_tasks(struct cpuset *cs,
              struct cpumask *new_cpus, nodemask_t *new_mems,
              bool cpus_updated, bool mems_updated)
 {
     if (cpumask_empty(new_cpus))
         cpumask_copy(new_cpus, parent_cs(cs)->effective_cpus);
     if (nodes_empty(*new_mems))
         *new_mems = parent_cs(cs)->effective_mems;
 
     spin_lock_irq(&callback_lock);
     cpumask_copy(cs->effective_cpus, new_cpus);
     cs->effective_mems = *new_mems;
     spin_unlock_irq(&callback_lock);
 
     if (cpus_updated)
         update_tasks_cpumask(cs);
     if (mems_updated)
         update_tasks_nodemask(cs);
 }
 
 static bool force_rebuild;
 
 void cpuset_force_rebuild(void)
 {
     force_rebuild = true;
 }
 
 /**
  * cpuset_hotplug_update_tasks - update tasks in a cpuset for hotunplug
  * @cs: cpuset in interest
  * @tmp: the tmpmasks structure pointer
  *
  * Compare @cs's cpu and mem masks against top_cpuset and if some have gone
  * offline, update @cs accordingly.  If @cs ends up with no CPU or memory,
  * all its tasks are moved to the nearest ancestor with both resources.
  */
 static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
 {
     static cpumask_t new_cpus;
     static nodemask_t new_mems;
     bool cpus_updated;
     bool mems_updated;
     struct cpuset *parent;
 retry:
     wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
 
     percpu_down_write(&cpuset_rwsem);
 
     /*
      * We have raced with task attaching. We wait until attaching
      * is finished, so we won't attach a task to an empty cpuset.
      */
     if (cs->attach_in_progress) {
         percpu_up_write(&cpuset_rwsem);
         goto retry;
     }
 
     parent = parent_cs(cs);
     compute_effective_cpumask(&new_cpus, cs, parent);
     nodes_and(new_mems, cs->mems_allowed, parent->effective_mems);
 
     if (cs->nr_subparts_cpus)
         /*
          * Make sure that CPUs allocated to child partitions
          * do not show up in effective_cpus.
          */
         cpumask_andnot(&new_cpus, &new_cpus, cs->subparts_cpus);
 
     if (!tmp || !cs->partition_root_state)
         goto update_tasks;
 
     /*
      * In the unlikely event that a partition root has empty
      * effective_cpus or its parent becomes erroneous, we have to
      * transition it to the erroneous state.
      */
     if (is_partition_root(cs) && (cpumask_empty(&new_cpus) ||
        (parent->partition_root_state == PRS_ERROR))) {
         if (cs->nr_subparts_cpus) {
             spin_lock_irq(&callback_lock);
             cs->nr_subparts_cpus = 0;
             cpumask_clear(cs->subparts_cpus);
             spin_unlock_irq(&callback_lock);
             compute_effective_cpumask(&new_cpus, cs, parent);
         }
 
         /*
          * If the effective_cpus is empty because the child
          * partitions take away all the CPUs, we can keep
          * the current partition and let the child partitions
          * fight for available CPUs.
          */
         if ((parent->partition_root_state == PRS_ERROR) ||
              cpumask_empty(&new_cpus)) {
             int old_prs;
 
             update_parent_subparts_cpumask(cs, partcmd_disable,
                                NULL, tmp);
             old_prs = cs->partition_root_state;
             if (old_prs != PRS_ERROR) {
                 spin_lock_irq(&callback_lock);
                 cs->partition_root_state = PRS_ERROR;
                 spin_unlock_irq(&callback_lock);
                 notify_partition_change(cs, old_prs, PRS_ERROR);
             }
         }
         cpuset_force_rebuild();
     }
 
     /*
      * On the other hand, an erroneous partition root may be transitioned
      * back to a regular one or a partition root with no CPU allocated
      * from the parent may change to erroneous.
      */
     if (is_partition_root(parent) &&
        ((cs->partition_root_state == PRS_ERROR) ||
         !cpumask_intersects(&new_cpus, parent->subparts_cpus)) &&
          update_parent_subparts_cpumask(cs, partcmd_update, NULL, tmp))
         cpuset_force_rebuild();
 
 update_tasks:
     cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
     mems_updated = !nodes_equal(new_mems, cs->effective_mems);
 
     if (mems_updated)
         check_insane_mems_config(&new_mems);
 
     if (is_in_v2_mode())
         hotplug_update_tasks(cs, &new_cpus, &new_mems,
                      cpus_updated, mems_updated);
     else
         hotplug_update_tasks_legacy(cs, &new_cpus, &new_mems,
                         cpus_updated, mems_updated);
 
     percpu_up_write(&cpuset_rwsem);
 }
 
 /**
  * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
  *
  * This function is called after either CPU or memory configuration has
  * changed and updates cpuset accordingly.  The top_cpuset is always
  * synchronized to cpu_active_mask and N_MEMORY, which is necessary in
  * order to make cpusets transparent (of no affect) on systems that are
  * actively using CPU hotplug but making no active use of cpusets.
  *
  * Non-root cpusets are only affected by offlining.  If any CPUs or memory
  * nodes have been taken down, cpuset_hotplug_update_tasks() is invoked on
  * all descendants.
  *
  * Note that CPU offlining during suspend is ignored.  We don't modify
  * cpusets across suspend/resume cycles at all.
  */
 static void cpuset_hotplug_workfn(struct work_struct *work)
 {
     static cpumask_t new_cpus;
     static nodemask_t new_mems;
     bool cpus_updated, mems_updated;
     bool on_dfl = is_in_v2_mode();
     struct tmpmasks tmp, *ptmp = NULL;
 
     if (on_dfl && !alloc_cpumasks(NULL, &tmp))
         ptmp = &tmp;
 
     percpu_down_write(&cpuset_rwsem);
 
     /* fetch the available cpus/mems and find out which changed how */
     cpumask_copy(&new_cpus, cpu_active_mask);
     new_mems = node_states[N_MEMORY];
 
     /*
      * If subparts_cpus is populated, it is likely that the check below
      * will produce a false positive on cpus_updated when the cpu list
      * isn't changed. It is extra work, but it is better to be safe.
      */
     cpus_updated = !cpumask_equal(top_cpuset.effective_cpus, &new_cpus);
     mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);
 
     /*
      * In the rare case that hotplug removes all the cpus in subparts_cpus,
      * we assumed that cpus are updated.
      */
     if (!cpus_updated && top_cpuset.nr_subparts_cpus)
         cpus_updated = true;
 
     /* synchronize cpus_allowed to cpu_active_mask */
     if (cpus_updated) {
         spin_lock_irq(&callback_lock);
         if (!on_dfl)
             cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
         /*
          * Make sure that CPUs allocated to child partitions
          * do not show up in effective_cpus. If no CPU is left,
          * we clear the subparts_cpus & let the child partitions
          * fight for the CPUs again.
          */
         if (top_cpuset.nr_subparts_cpus) {
             if (cpumask_subset(&new_cpus,
                        top_cpuset.subparts_cpus)) {
                 top_cpuset.nr_subparts_cpus = 0;
                 cpumask_clear(top_cpuset.subparts_cpus);
             } else {
                 cpumask_andnot(&new_cpus, &new_cpus,
                            top_cpuset.subparts_cpus);
             }
         }
         cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
         spin_unlock_irq(&callback_lock);
         /* we don't mess with cpumasks of tasks in top_cpuset */
     }
 
     /* synchronize mems_allowed to N_MEMORY */
     if (mems_updated) {
         spin_lock_irq(&callback_lock);
         if (!on_dfl)
             top_cpuset.mems_allowed = new_mems;
         top_cpuset.effective_mems = new_mems;
         spin_unlock_irq(&callback_lock);
         update_tasks_nodemask(&top_cpuset);
     }
 
     percpu_up_write(&cpuset_rwsem);
 
     /* if cpus or mems changed, we need to propagate to descendants */
     if (cpus_updated || mems_updated) {
         struct cpuset *cs;
         struct cgroup_subsys_state *pos_css;
 
         rcu_read_lock();
         cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
             if (cs == &top_cpuset || !css_tryget_online(&cs->css))
                 continue;
             rcu_read_unlock();
 
             cpuset_hotplug_update_tasks(cs, ptmp);
 
             rcu_read_lock();
             css_put(&cs->css);
         }
         rcu_read_unlock();
     }
 
     /* rebuild sched domains if cpus_allowed has changed */
     if (cpus_updated || force_rebuild) {
         force_rebuild = false;
         rebuild_sched_domains();
     }
 
     free_cpumasks(NULL, ptmp);
 }
 
 void cpuset_update_active_cpus(void)
 {
     /*
      * We're inside cpu hotplug critical region which usually nests
      * inside cgroup synchronization.  Bounce actual hotplug processing
      * to a work item to avoid reverse locking order.
      */
     schedule_work(&cpuset_hotplug_work);
 }
 
 void cpuset_wait_for_hotplug(void)
 {
     flush_work(&cpuset_hotplug_work);
 }
 
 /*
  * Keep top_cpuset.mems_allowed tracking node_states[N_MEMORY].
  * Call this routine anytime after node_states[N_MEMORY] changes.
  * See cpuset_update_active_cpus() for CPU hotplug handling.
  */
 static int cpuset_track_online_nodes(struct notifier_block *self,
                 unsigned long action, void *arg)
 {
     schedule_work(&cpuset_hotplug_work);
     return NOTIFY_OK;
 }
 
 static struct notifier_block cpuset_track_online_nodes_nb = {
     .notifier_call = cpuset_track_online_nodes,
     .priority = 10,     /* ??! */
 };
 
 /**
  * cpuset_init_smp - initialize cpus_allowed
  *
  * Description: Finish top cpuset after cpu, node maps are initialized
  */
 void __init cpuset_init_smp(void)
 {
     /*
      * cpus_allowd/mems_allowed set to v2 values in the initial
      * cpuset_bind() call will be reset to v1 values in another
      * cpuset_bind() call when v1 cpuset is mounted.
      */
     top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;
 
     cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
     top_cpuset.effective_mems = node_states[N_MEMORY];
 
     register_hotmemory_notifier(&cpuset_track_online_nodes_nb);
 
     cpuset_migrate_mm_wq = alloc_ordered_workqueue("cpuset_migrate_mm", 0);
     BUG_ON(!cpuset_migrate_mm_wq);
 }
 
 /**
  * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset.
  * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
  * @pmask: pointer to struct cpumask variable to receive cpus_allowed set.
  *
  * Description: Returns the cpumask_var_t cpus_allowed of the cpuset
  * attached to the specified @tsk.  Guaranteed to return some non-empty
  * subset of cpu_online_mask, even if this means going outside the
  * tasks cpuset.
  **/
 
 void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 {
     unsigned long flags;
 
     spin_lock_irqsave(&callback_lock, flags);
     guarantee_online_cpus(tsk, pmask);
     spin_unlock_irqrestore(&callback_lock, flags);
 }
 
 /**
  * cpuset_cpus_allowed_fallback - final fallback before complete catastrophe.
  * @tsk: pointer to task_struct with which the scheduler is struggling
  *
  * Description: In the case that the scheduler cannot find an allowed cpu in
  * tsk->cpus_allowed, we fall back to task_cs(tsk)->cpus_allowed. In legacy
  * mode however, this value is the same as task_cs(tsk)->effective_cpus,
  * which will not contain a sane cpumask during cases such as cpu hotplugging.
  * This is the absolute last resort for the scheduler and it is only used if
  * _every_ other avenue has been traveled.
  *
  * Returns true if the affinity of @tsk was changed, false otherwise.
  **/
 
 bool cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
     const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
     const struct cpumask *cs_mask;
     bool changed = false;
 
     rcu_read_lock();
     cs_mask = task_cs(tsk)->cpus_allowed;
     if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask)) {
         do_set_cpus_allowed(tsk, cs_mask);
         changed = true;
     }
     rcu_read_unlock();
 
     /*
      * We own tsk->cpus_allowed, nobody can change it under us.
      *
      * But we used cs && cs->cpus_allowed lockless and thus can
      * race with cgroup_attach_task() or update_cpumask() and get
      * the wrong tsk->cpus_allowed. However, both cases imply the
      * subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr()
      * which takes task_rq_lock().
      *
      * If we are called after it dropped the lock we must see all
      * changes in tsk_cs()->cpus_allowed. Otherwise we can temporary
      * set any mask even if it is not right from task_cs() pov,
      * the pending set_cpus_allowed_ptr() will fix things.
      *
      * select_fallback_rq() will fix things ups and set cpu_possible_mask
      * if required.
      */
     return changed;
 }
 
 void __init cpuset_init_current_mems_allowed(void)
 {
     nodes_setall(current->mems_allowed);
 }
 
 /**
  * cpuset_mems_allowed - return mems_allowed mask from a tasks cpuset.
  * @tsk: pointer to task_struct from which to obtain cpuset->mems_allowed.
  *
  * Description: Returns the nodemask_t mems_allowed of the cpuset
  * attached to the specified @tsk.  Guaranteed to return some non-empty
  * subset of node_states[N_MEMORY], even if this means going outside the
  * tasks cpuset.
  **/
 
 nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
 {
     nodemask_t mask;
     unsigned long flags;
 
     spin_lock_irqsave(&callback_lock, flags);
     rcu_read_lock();
     guarantee_online_mems(task_cs(tsk), &mask);
     rcu_read_unlock();
     spin_unlock_irqrestore(&callback_lock, flags);
 
     return mask;
 }
 
 /**
  * cpuset_nodemask_valid_mems_allowed - check nodemask vs. current mems_allowed
  * @nodemask: the nodemask to be checked
  *
  * Are any of the nodes in the nodemask allowed in current->mems_allowed?
  */
 int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
 {
     return nodes_intersects(*nodemask, current->mems_allowed);
 }
 
 /*
  * nearest_hardwall_ancestor() - Returns the nearest mem_exclusive or
  * mem_hardwall ancestor to the specified cpuset.  Call holding
  * callback_lock.  If no ancestor is mem_exclusive or mem_hardwall
  * (an unusual configuration), then returns the root cpuset.
  */
 static struct cpuset *nearest_hardwall_ancestor(struct cpuset *cs)
 {
     while (!(is_mem_exclusive(cs) || is_mem_hardwall(cs)) && parent_cs(cs))
         cs = parent_cs(cs);
     return cs;
 }
 
 /*
  * __cpuset_node_allowed - Can we allocate on a memory node?
  * @node: is this an allowed node?
  * @gfp_mask: memory allocation flags
  *
  * If we're in interrupt, yes, we can always allocate.  If @node is set in
  * current's mems_allowed, yes.  If it's not a __GFP_HARDWALL request and this
  * node is set in the nearest hardwalled cpuset ancestor to current's cpuset,
  * yes.  If current has access to memory reserves as an oom victim, yes.
  * Otherwise, no.
  *
  * GFP_USER allocations are marked with the __GFP_HARDWALL bit,
  * and do not allow allocations outside the current tasks cpuset
  * unless the task has been OOM killed.
  * GFP_KERNEL allocations are not so marked, so can escape to the
  * nearest enclosing hardwalled ancestor cpuset.
  *
  * Scanning up parent cpusets requires callback_lock.  The
  * __alloc_pages() routine only calls here with __GFP_HARDWALL bit
  * _not_ set if it's a GFP_KERNEL allocation, and all nodes in the
  * current tasks mems_allowed came up empty on the first pass over
  * the zonelist.  So only GFP_KERNEL allocations, if all nodes in the
  * cpuset are short of memory, might require taking the callback_lock.
  *
  * The first call here from mm/page_alloc:get_page_from_freelist()
  * has __GFP_HARDWALL set in gfp_mask, enforcing hardwall cpusets,
  * so no allocation on a node outside the cpuset is allowed (unless
  * in interrupt, of course).
  *
  * The second pass through get_page_from_freelist() doesn't even call
  * here for GFP_ATOMIC calls.  For those calls, the __alloc_pages()
  * variable 'wait' is not set, and the bit ALLOC_CPUSET is not set
  * in alloc_flags.  That logic and the checks below have the combined
  * affect that:
  *  in_interrupt - any node ok (current task context irrelevant)
  *  GFP_ATOMIC   - any node ok
  *  tsk_is_oom_victim   - any node ok
  *  GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
  *  GFP_USER     - only nodes in current tasks mems allowed ok.
  */
 bool __cpuset_node_allowed(int node, gfp_t gfp_mask)
 {
     struct cpuset *cs;      /* current cpuset ancestors */
     bool allowed;           /* is allocation in zone z allowed? */
     unsigned long flags;
 
     if (in_interrupt())
         return true;
     if (node_isset(node, current->mems_allowed))
         return true;
     /*
      * Allow tasks that have access to memory reserves because they have
      * been OOM killed to get memory anywhere.
      */
     if (unlikely(tsk_is_oom_victim(current)))
         return true;
     if (gfp_mask & __GFP_HARDWALL)  /* If hardwall request, stop here */
         return false;
 
     if (current->flags & PF_EXITING) /* Let dying task have memory */
         return true;
 
     /* Not hardwall and node outside mems_allowed: scan up cpusets */
     spin_lock_irqsave(&callback_lock, flags);
 
     rcu_read_lock();
     cs = nearest_hardwall_ancestor(task_cs(current));
     allowed = node_isset(node, cs->mems_allowed);
     rcu_read_unlock();
 
     spin_unlock_irqrestore(&callback_lock, flags);
     return allowed;
 }
 
 /**
  * cpuset_mem_spread_node() - On which node to begin search for a file page
  * cpuset_slab_spread_node() - On which node to begin search for a slab page
  *
  * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for
  * tasks in a cpuset with is_spread_page or is_spread_slab set),
  * and if the memory allocation used cpuset_mem_spread_node()
  * to determine on which node to start looking, as it will for
  * certain page cache or slab cache pages such as used for file
  * system buffers and inode caches, then instead of starting on the
  * local node to look for a free page, rather spread the starting
  * node around the tasks mems_allowed nodes.
  *
  * We don't have to worry about the returned node being offline
  * because "it can't happen", and even if it did, it would be ok.
  *
  * The routines calling guarantee_online_mems() are careful to
  * only set nodes in task->mems_allowed that are online.  So it
  * should not be possible for the following code to return an
  * offline node.  But if it did, that would be ok, as this routine
  * is not returning the node where the allocation must be, only
  * the node where the search should start.  The zonelist passed to
  * __alloc_pages() will include all nodes.  If the slab allocator
  * is passed an offline node, it will fall back to the local node.
  * See kmem_cache_alloc_node().
  */
 
 static int cpuset_spread_node(int *rotor)
 {
     return *rotor = next_node_in(*rotor, current->mems_allowed);
 }
 
 int cpuset_mem_spread_node(void)
 {
     if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
         current->cpuset_mem_spread_rotor =
             node_random(&current->mems_allowed);
 
     return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
 }
 
 int cpuset_slab_spread_node(void)
 {
     if (current->cpuset_slab_spread_rotor == NUMA_NO_NODE)
         current->cpuset_slab_spread_rotor =
             node_random(&current->mems_allowed);
 
     return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
 }
 
 EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);
 
 /**
  * cpuset_mems_allowed_intersects - Does @tsk1's mems_allowed intersect @tsk2's?
  * @tsk1: pointer to task_struct of some task.
  * @tsk2: pointer to task_struct of some other task.
  *
  * Description: Return true if @tsk1's mems_allowed intersects the
  * mems_allowed of @tsk2.  Used by the OOM killer to determine if
  * one of the task's memory usage might impact the memory available
  * to the other.
  **/
 
 int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
                    const struct task_struct *tsk2)
 {
     return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
 }
 
 /**
  * cpuset_print_current_mems_allowed - prints current's cpuset and mems_allowed
  *
  * Description: Prints current's name, cpuset name, and cached copy of its
  * mems_allowed to the kernel log.
  */
 void cpuset_print_current_mems_allowed(void)
 {
     struct cgroup *cgrp;
 
     rcu_read_lock();
 
     cgrp = task_cs(current)->css.cgroup;
     pr_cont(",cpuset=");
     pr_cont_cgroup_name(cgrp);
     pr_cont(",mems_allowed=%*pbl",
         nodemask_pr_args(&current->mems_allowed));
 
     rcu_read_unlock();
 }
 
 /*
  * Collection of memory_pressure is suppressed unless
  * this flag is enabled by writing "1" to the special
  * cpuset file 'memory_pressure_enabled' in the root cpuset.
  */
 
 int cpuset_memory_pressure_enabled __read_mostly;
 
 /*
  * __cpuset_memory_pressure_bump - keep stats of per-cpuset reclaims.
  *
  * Keep a running average of the rate of synchronous (direct)
  * page reclaim efforts initiated by tasks in each cpuset.
  *
  * This represents the rate at which some task in the cpuset
  * ran low on memory on all nodes it was allowed to use, and
  * had to enter the kernels page reclaim code in an effort to
  * create more free memory by tossing clean pages or swapping
  * or writing dirty pages.
  *
  * Display to user space in the per-cpuset read-only file
  * "memory_pressure".  Value displayed is an integer
  * representing the recent rate of entry into the synchronous
  * (direct) page reclaim by any task attached to the cpuset.
  */
 
 void __cpuset_memory_pressure_bump(void)
 {
     rcu_read_lock();
     fmeter_markevent(&task_cs(current)->fmeter);
     rcu_read_unlock();
 }
 
 #ifdef CONFIG_PROC_PID_CPUSET
 /*
  * proc_cpuset_show()
  *  - Print tasks cpuset path into seq_file.
  *  - Used for /proc/<pid>/cpuset.
  *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
  *    doesn't really matter if tsk->cpuset changes after we read it,
  *    and we take cpuset_rwsem, keeping cpuset_attach() from changing it
  *    anyway.
  */
 int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
              struct pid *pid, struct task_struct *tsk)
 {
     char *buf;
     struct cgroup_subsys_state *css;
     int retval;
 
     retval = -ENOMEM;
     buf = kmalloc(PATH_MAX, GFP_KERNEL);
     if (!buf)
         goto out;
 
     css = task_get_css(tsk, cpuset_cgrp_id);
     retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
                 current->nsproxy->cgroup_ns);
     css_put(css);
     if (retval >= PATH_MAX)
         retval = -ENAMETOOLONG;
     if (retval < 0)
         goto out_free;
     seq_puts(m, buf);
     seq_putc(m, '\n');
     retval = 0;
 out_free:
     kfree(buf);
 out:
     return retval;
 }
 #endif /* CONFIG_PROC_PID_CPUSET */
 
 /* Display task mems_allowed in /proc/<pid>/status file. */
 void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
 {
     seq_printf(m, "Mems_allowed:\t%*pb\n",
            nodemask_pr_args(&task->mems_allowed));
     seq_printf(m, "Mems_allowed_list:\t%*pbl\n",
            nodemask_pr_args(&task->mems_allowed));
 }